Because the dies are used to make wax preforms of the finished casting. The actual mold for the finished metal part is made out of plaster which covers and surrounds the preforms and whatever wax feed gates that are attached to them. Then the entire "flask" of wax preforms and plaster are baked in an oven during which the wax melts and runs out. This leaves a hollow cavity in the mold which can then be filled with molten metal. After the metal cools and solidifies the plaster is removed in pieces and discarded. The castings are cut away from the gate structure and any bits of plaster stuck on them scraped or polished away.
Note that when metal cools and solidifies it shrinks a few percent (called the "percent shrink"). Therefore the wax preforms made in the aluminum mold are actually that percentage oversize from the desired finish size of the casting.
Thanks buddy...but u went more far...i m jst thinkin of replacing that aluminum die with any other metal or plastic or in short any other material...So wht do u think it's possible...?
And yes, I agree with Nickname. You are well advised to communicate on these issues in a recognized formal language that can be understood by others and logically translated into English for the benefit of the participants in this forum. If your needs are so trivial that you cannot meet this reasonable requirement then you are hardly worth the time that others would offer to you. And now for the benefit of others who may view this topic and even you if you can understand what is written I offer the following:
The short answer (to "What materials can be used for investment casting dies?") is just about any material that can be molded around a master pattern or machined, carved or whatever to the shape you want. Of course the mold material will have to withstand the temperature of the melted wax without losing its shape. And the wax mold will have to be durable enough to withstand as much use as required for the intended production volume. This is a factor that favors aluminum over silicone rubber, a common wax mold material. Best you learn a lot more about this process and seek out the professional advice of someone with whom you are willing to discuss the specifics of your particular needs.
The long answer can be found at this web site (among others):
44 Worthington Road . Cranston, RI 02920 . Email:
info@cranstoncasting.com
phone: 401-467-8184 . fax: 401-467-CAST
The Lost Wax Casting Process dates back to early Egypt and
later in China during the Chang Dynasty, 1776-1122 BC. The Lost Wax Casting
Process was used mainly to reproduce metal parts and to reduce the time and
labor needed for producing parts in quantity by metal smiths. Molten metal was
poured into molds and removed when solidified. Since then modern technology has
made the metal smith basically extinct.
The Lost Wax Casting Process has basically five steps to
produce a raw casting. A craft process, all the steps in the Lost Wax Casting
Process are equally important. Today's technology enables us to mold, wax, and
cast a smoother, more intricate and complex part, with more precision than ever
before
Model:
A model is a metal
pattern of the design to be reproduced. It is made 5% larger than the finished
casting product. A hard metal is used to withstand the temperatures required
for vulcanizing molds. There are many ways to create a model. The customer can
realize a significant cost saving and insure a quality casting by consulting
with an experienced caster who is aware of current advancements and methods of
production. Common modifications may involve undercuts, shrinkage,
thickness/thinness, and temperature uniformity.
Molding:
Most molds
consist of two parts which create a negative cavity of the design which will be
cast. Wax or plastic is injected into the mold to make a positive copy. Molds
are made of various types of rubbers, metals, plastics or plasters. Vulcanized
rubber is the most common and is the least expensive. It requires the model to
be 5% larger. The mold must be able to withstand a temperature of 350 degrees
Fahrenheit. Minimum size rubber mold is 3" long x 2" wide x 1/2"
thickness. Maximum size rubber mold is 10" long x 6" wide x 6"
thickness.
Waxes:
The Wax pattern
is a positive copy of the design to be transferred into metal. The waxes or
plastics are produced by injecting material directly into the cavity of the
mold. It is recommended however, that samples be made to insure a proper
burnout for a clean surface before the beginning production. A minimum
thickness of .040 is required for proper fluidity. The maximum wax is 10"
long, 5" wide, and 5" thick.
Investment Mold:
The Investment
mold is a negative copy of the wax pattern. Investment powder, a form of
plaster. is mixed with water, and poured as a liquid directly over the wax
pattern to make an exact negative mold of the wax design. There are many types
of investments. The right investment depends on the way waxes will be treed and
grouped inside the flask and the metal which will be used. Once the investment
becomes solid over the waxes, the mold is put into ovens to remove all of the
wax and cure the investment.
Casting:
Castings are
exact metal copies of the mold or wax chosen to be reproduced. The two most
common casting techniques are centrifugal casting and vacuum assist casting.
Both processes have special requirements for a quality casting, gating and
venting being the most common. As a general rule filigree and thinner pieces
are more successfully cast centrifugally and heavier, thicker pieces are
produced in a vacuum assist process. Our minimum thickness is .040 and our
maximum weight per piece is 10 lbs.
Investment Casting Dies
Re: Investment Casting Dies
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