Last month's newsletter showed how
the Unicast Process can be incorporated into rubber tire
mold manufacturing to reduce the amount of finish
machining and lower the overall cost of the molds. If
you missed it, you can view it again by clicking
HERE .
This month we look at how the Unicast Process differs
from Investment Casting, or the Lost Wax process
Precision casting is not a new concept.
Most references list the lost wax method as being
approximately 6000 years old for sculptures and jewelry.
But over the past 100 years, the process has undergone a
series of modernizations to apply the technique to more
industrial applications with the largest advances occurring
in the aerospace fields. As the process was applied to
these high precision applications, it became more widely
accepted as the process to turn to when smooth surface
finishes or high precision were required. However, due
to the nature of the process, it has its limitations when
dealing with larger parts or short runs. These
limitations create a gap between the size and volume
suitability of traditional sand processes and the precision
offered by investment casting. Unicast fills this gap.
Where are the major differences?
Between Unicast and Sand Processes
the difference is primarily in materials. The Unicast
process typically allows for the same patterns that are used
for sand to be used with Unicast. Unicast does not
shrink, expand, or generate heat during molding - so
patterns can be of virtually any materials - including
SLA/STL patterns, rubber, wood, metal, epoxy, etc.
Techniques for mold assembly are also quite similar in that
a cope and drag are typical and the same gates, risers, and
runner configurations can be used.
Between Unicast and Investment Casting
the difference is primarily in how the pattern is used.
The Unicast process uses a pattern that can be re-used over
and over again as in sand casting. The materials used
in the mold are very similar which is why the same surface
finishes and accuracies can be obtained from Unicast as
Investment Casting. However, with Investment Casting it is
necessary to create a pattern for every casting made.
This is typically done with dies and molds that will accept
a wax that will be encapsulated into the ceramic investment.
These dies and molds are typically machined at high expense
and lead time and require an injection machine to fill the
cavities created by these molds. Additionally, the process
of building a shell around these patterns requires a series
of dip tanks and drying areas that consume a decent amount
of shop space. Finally, once the mold is made - the
pattern now needs to be removed from the ceramic shell which
is done either through boiling solutions or autoclaves - for
even more equipment.
A pattern of wax also is also one of the
key limiting factors in making a large investment casting.
There are two problems with a large wax pattern.
First, such a large pattern has a significant mass and the
strength of the wax does not allow for it to support itself
well. This causes problems with the wax pattern
maintaining its original dimensions and also complicates the
assembly of such a pattern onto trees. Second, when
the wax is heated up to be removed, it is subject to thermal
expansion. When the wax is so large, it takes a longer
time for the heat to transfer into the wax body which allows
the wax time to expand. An expanding wax pattern
causes the shell to break.
It needs to be stated that Investment
Casting has its applications. When high volume,
smaller, highly accurate castings are required - and the
cost of the molds, inventory, equipment and processing time
can be amortized across a large number of parts - it is the
practical solution. However, our goal is to raise
awareness that when you do not have so many parts to spread
the costs over, or you have a large piece to cast - you do
not have to give up on precision casting. Turn to
Unicast as this is precisely the niche the process operates
best within.
What are the applications?
The greatest applications where Unicast
performs best over Investment Casting are those applications
that Investment Casting is handicapped in.
Specifically where sizes are larger and volumes are smaller.
Precision Tooling & Molds
Large Castings
Sculptures
Regular readers of the newsletter are
also aware of the applications for ceramic cores
specifically for pump and valve components. More
information about how the process is used for coremaking can
be found on our site
here or by
requesting further information.
Do you have a piece that requires a
precision casting? Don't turn to machining and don't
make the investment in molds, equipment, and tooling that
you may not need to. Hey - it's called
investment casting for a reason! Contact us
for more information on how Unicast can bridge your
processing gap.
