In a message dated 98-03-24 17:17:06 EST, you write:
<< Subj: Delrin Molds
Date: 98-03-24 17:17:06 EST
From: kelly@satellitemodels.com (Kelly Hand)
Sender: owner-rp-ml@bart.lpt.fi
To: rp-ml@bart.lpt.fi
Dear list,
I am interested in learning roughly how many cast epoxy parts one can
expect to get out of a machined delrin mold. The epoxy is very low
viscosity (like water, I'm told) and the part geometry is going to be
fairly forgiving (generous draft and no small features, or so I'm told) and
small, roughly half the size of a small beeper. The molds will probably be
heated to accelerate curing.
Any insights would be appreciated.
Kelly Hand
Satellite Models
950 Rengstorff Ave. Ste. C
Mountain View, CA. 94043
650-903-3540 >>
In a message dated 98-03-24 23:34:53 EST, you write:
<< ubj: Re: Delrin Molds
Date: 98-03-24 23:34:53 EST
From: mark-s@inav.net (markschanze)
Sender: owner-rp-ml@bart.lpt.fi
Reply-to: @inav.net
To: rp-ml@bart.lpt.fi (RP mail list)
We in the industry use silicone to mold because it naturally self-releases.
Machinable plastics such as polypropylene also have self-releasing
characteristics. Polypropylene is not easy to machine due to it's low melt
temperature. Delrin is easier to machine but certain grades still create
lots of "hair" or melt build up on the cutter. The easier the material is
to cut and the better the cutting finish the less natural release
characteristics the material will have. Polypropylene will have an
unlimited mold life. Delrin will have a limited mold life. Therefore the
release agent one uses will determine the life of the mold. Delrin will
not take most release agents well. Since you are trying to mold from a
material that will ultimately be dependant upon the release agent used,
maybe a material that handles release agents well should be considered,
like aluminum. Machining aluminum versus delrin and expecting to hold
tolerances is a no brainer. Finishing delrin is a bitch! Freekote 700
from Dextor Hysol is a great release agent for aluminum. Depending on the
tolerances required I would prefer silicone. At the most I would build a
hybrid mold of machined aluminum for high toleranced features and encompass
the fixtures in silicone. Obviously I could go on for a while so I will
stop. Questions?
Mark Schanze
Molding Technology Manager
CIVCO Medical Instruments
319 656 4447
marks@civcomedical.com >>
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Hello all,
Since we have extensive experience in machining various grades of polypro,
Delrin and aluminum among others, here is my $.02....
While I agree with Mark somewhat in that Delrin is typically a better
candidate for machining than polypropylene. Since polypro is not as rigid as
Delrin, special steps must be taken to hold the workpeice and a more cautious
machining approach needs to be taken.
It is not entirely correct however, that Delrin itself poses a problem with
machining due to buildup on the cutting tool. Just about ANY material
including: aluminum, steel, or other plastic will act similarly. Material
will build up on the cutter if the workpiece is not properly machined.
You may want to consider these PRO and CON issues as well.
They relate to machining molds from Delrin VS. Aluminum.....
DELRIN
PRO:
Machining Delrin with a cutting tool is ~20% faster than aluminum HOWEVER-
-this is only true with a Very High Speed machining center. A good operator
and programmer will machine them out of either material in
-this does not mean the process cycle is shorter either
CON:
Cannot be machined as accurately as aluminum
Cannot be machined as reliably as aluminum
Cannot be EDM'd (electrical discharge machining)
-MANY critical features Cannot Be Machined
Engineering changes requiring material addition Cannot Be Made
Does not yield as very good surface finish
Cannot be textured
Extensive hand fininshing is often required
Molded parts are not as precise as machined aluminum tooling
Molded parts are not as reliable as machined aluminum tooling
(a separate issue from accuracy and precision of machined workpiece)
Tool life is very short
Delrin stock is more expensive than aluminum
THE BOTTOM _________________
In many instances protoype and even pre-production tooling can be machined
from aluminum and steel in comparable lead times. We do it all the time.
Catch you all later.
BTW-
Do we have anyone from Ireland on this list?
Best Regards,
Ron Ptaszek
P&R Precision, Inc.
50495 Corporate Drive
Shelby Township, MI 48315
for Rapid turn Injection Molds....
TEL: 810-254-6720
<A HREF="mailto:Ron@InjectionMolds.com">Ron@InjectionMolds.com</A>
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