RE: [rp-ml] SLS Powder Life - example situation.

Another thought concerning powder decay (polyamide) in an SLS machine.

What happens if you run a "build" but don't build anything?

I mean . .you run a build . .a full height (17 inch or whatever it is) build
with normal temperature settings, but don't sinter anything. You never turn
on the laser.

And lets say to make it interesting . . . you turn on your minimum layer
time to a minute or two.

After a very long build . . .. you are going to have a tall partcake with
no parts in it and some full overflow bins.

Has the powder in either of these locations degraded, and if so, by how
much?

All opinions appreciated.

Scott Tilton
 

-----Original Message-----
From: Scott Tilton [mailto:stilton@protoprod.com]
Sent: Wednesday, June 23, 2004 4:23 PM
To: rp-ml@rapid.lpt.fi
Subject: [rp-ml] SLS Powder Life - example situation.

So a co-worker of mine is explaining to some folks about the recycleability
of SLS powder.

He started expressing the age of the powder in terms of how many times it
has cycled through the machine. (how many times the powder has been in a
partcake)

When he asked me for confirmation, I said that he was basically right, but
that I thought a measure of HOW LONG the powder had been in a partcake was
more relevant than the number of times it had cycled through the machine.

I got somewhat of a dismissive look and a general blow off with a statement
like "yes, there are many of other minor factors that affect the degredation
of the powder."
(mental note, don't correct boss in front of visitors)

Later I was asked to explain what I meant and I used an example:

Say you are building a bunch of parts that can be arranged in a nice 2"
layer in the partcake.
You need to build as many of these parts as you can with a the material you
have on hand - which happens to be just enough to completely fill the feeds
on your machine (2500+ in my case)

In one extreme, you could load up the machine and run 7 of the two inch
"layers" of parts all in one tall build.

In another extreme, you could just probably run 5 or 6 builds, each of which
only had one "layer" of parts.

My boss says this second example would be stupid thing to do. You'd waste
the powder on the warm up and cool down layers. (and if you use a heat
fence . . . you'd waste those sacrificial parts each time)

I wasn't so sure.

I mean . . . say that the 2 inch tall "layer" of parts requires 5 hours of
build time.
Run that 7 layer partcake and the powder in the bottom of the build has been
in there cooking for somewhere over 30 hours.
30+ hours being maintained at that high partcake temperature.

The individual part layer builds each only subjected the powder to the high
partcake temperatures for around 5 hours.

At then end of the two examples . . . you may have one or two layers more
parts by running them in the single build, but your powder seems like it'd
be more aged / degraded to me.

Yes I know . . . there are other cost factors . . setup time, and the
material wasted by warm up and cool down stages, exactly how hot is your
partcake/cylinder/ piston heaters etc.
But remember . . I was only talking about maximizing the life of your
powder.

Anyone have any opinions on this topic they'd like to share.
Heck, maybe some of you hardcore SLS'ers (like you melt flow indexers out
there) have data to support your opinions.

Assuming you've read this far . .thanks for your attention.
Hope this doesn't open me up to another FLOOD of spam.

Scott Tilton
Received on Thu Jun 24 16:54:18 2004