Rapid Molds - RE: from Delrin

From: PnR Molds (PnRMolds@aol.com)
Date: Wed Mar 25 1998 - 19:25:19 EET

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 >>


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.....


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


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.

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....
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TEL: 810-254-6720
FAX: 810-254-0638

<A HREF="mailto:Ron@InjectionMolds.com">Ron@InjectionMolds.com</A>

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