RE: Rapid Mold Making

From: Vicki Billings (
Date: Fri Nov 14 1997 - 19:46:38 EET

Hi Pedro,

In response to your question asking if LOM can be used for direct
investment casting. Yes, LomPaper masters can and have been used as a
one-to-one replacement for wax masters for direct investment casting.
LOM can also be used a mold for indirect investment casting, in which
case roughly 100 wax patterns can be injected into the LOM mold.

One advantage of using the LOM process for direct investment casting is
that the low thermal expansion coefficient of paper (and the low
softening point of the adhesive) allow the LOM pattern to collapse and
prevent the casting shell from cracking during heating.

Some cautions - LOMPaper masters are different from wax and need to be
treated differently. To prevent moisture incursion (from the ceramic
slurry used in the casting process) into the LOM master, a coating
should be applied to the master. Acrylic enamel clear coat is a good
choice as it leaves little ash or residue.

Temperatures greater than 574o C in an oxidizing environment are
required to extract the master. There will be residual ash and the ash
can be either blown out of the shell with compressed air or flushed out
with water.

I don't know your specific requirements, but you might want to consider
indirect investment casting, especially if you are creating many
duplicates. Fabricating a single LOM mold and injecting wax into it to
create hundreds of duplicates is an very economical process.

For more detail information, I recommend an article in Prototyping
Technology International '97 (p.184) - Prototype Tooling and Low Volume
Manufacturing Through Laminated Object Manufacturing (LOM) by Sung Pak,
et. al. I also recommend a masters thesis by Brian Hinckley presented
to the Dept. of Manufacturing Engineering and Engineering Technology at
Brigham Young University (Utah, USA) and entitled Direct Investment
Casting of LOM (Laminated Object Manufacturing) Rapid Prototypes.

Best of luck with your endeavors.

Vicki Billings
Director of Marketing
Helisys, Inc.
24015 Garnier Street
Torrance, CA 90505 USA
310-891-0600 x-242
310-891-0626 FAX

>From: Pedro Garayo Olarra[]
>Sent: Thursday, November 13, 1997 8:35 PM
>To: rapid prototyping mailing list
>Subject: Rapid Mold Making
>Hi rpmlers,
>I have some questions related to rapid mold making techniques. I'm only
>interested on injection molding, but any help on other molding process is
>Specially, I'm interested in direct tooling methods and any bridge
>tooling method.
>What's the most probable failure mechanism for a cavitie made of resin
>(epoxi or PU)? Is it fatigue, impact at the gate ...? And for a cavities
>made of Aluminum or any other alloy (Cu-Be, Zn-Al...)?
>Is LOM used to make master patterns for investment casting?
>How good is 3DPrinting for Investment casting?
>Where can I find info on RTV processes?
>What are the main problems in using Spray metal and any back filling to
>make molds? Again, what's the most probable failure mechanism?
>Pedro Garayo
>Research Engineer
>Parque Tecnologico de Boecillo.P 209.
>Boecillo 47151 Valladolid. SPAIN.
>tel: 34-83-548035
>fax: 34-83-548062

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