Ceramic mold inserts


Jim King <jimking3@...>
 

Ceramic inserts made via the SLA process are in their infancy. They are
so new to the RP world that very little info is available regarding life
expectancy, materials shot or geometry types that have been successfully
(or not) produced. The comments re: tooling costs still being closely
tied with traditional mold making (setting inserts, putting in ejector
pins, cutting runners, drilling gates, etc.) are very true. While the
core/cavity geometry is a major part of the mold making process, the
other "stuff" takes almost as much time to generate, depending on what
you're making. And, yes, replacing a cracked set of inserts or making a
new set of inserts because you goofed on shrinkage calculations or left
out a feature is far cheaper and faster than having to remake a hunk of
steel!

I **do** know from info provided so far that small geometry parts, like
needle tips with .005" radius, have been shot successfully using long
fiber-glass PP without any significant cavity breakdown. The molder
told me he got 1500 shots (in a 4 cavity mold) before the gate corners
and a small piece of text started wearing. With non-hostile materials,
like the styrene we all love, I expect longer mold life is likely. As
for "what" can be shot, the detail is strictly a matter of size,
geometry and the affects of the SLA layering process. Parts like wagon
wheels and driver centers could be candidates since the spokes on each
are elliptically shaped. Small features, like text, will likely be the
first victims of mold wear, according to my SLA house, as a result of
the plastic shrinking around the feature(s) and pulling it/them off
after repeated cycles.

There is no single method available to produce the quality we require in
our kits. Manufacturers are constantly pushing the envelope to use the
best methods available yet trying to keep affordability in check. As
was correctly stated, China's labor is getting higher by the day but
it's still far cheaper to send parts to China, have them assembled and
pad printed, then returned RTR in a pretty box than to do that here.
Kits are fast disappearing from hobby shelves. I've been told by 2 well
known dealers not to even bother trying to sell them a urethane flat kit
.. there's simply no market in their stores. The only way I can keep up
with the Jones' is to offer 1-pc bodies (cast bodies, not assembled flat
panels) and use RP to produce detailed patterns that can't be made any
other way. Perhaps ceramic inserts can be the next tool in our arsenal.

I applaud any discussion on this topic but I can only speak in
generalities, so please don't get upset when I won't answer questions
about specific methods or sources I use. I have no problem sharing
information when it will be used by hobbiests but when it can be used by
another manufacturer, that's where I have to stop. RP is my livelihood
and I won't jeopardize my family's well-being just to answer seemingly
harmless questions.

Jim King
Smoky Mountain Model Works, Inc.
http://www.smokymountainmodelworks.com/

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