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Using several
different types
of patterns
Texcast can
produce
investment
castings for
prototype or
production.
At Texcast it is
very common to
use different
methods to
produce the
patterns
depending upon
the delivery and
maturity of
design. New
designs are
often prototyped
to allow testing
of an actual
investment
casting. Once
this has been
done hard
tooling is
normally built,
but not always.
We produce many
parts using
several methods
other than hard
tooling once
parts go into
production.
There is not
really any
difference
between rapid
prototyping,
rapid
production,
direct
manufacturing
and rapid
manufacturing of
investment
castings other
than which type
of pattern is
most appropriate
to meet
delivery,
quality,
quantity and
cost
constraints.
There are no set
limits as to
which process to
use based upon
the number of
parts to be
produced. Each
part
configuration is
unique and must
be reviewed by
foundry to
determine the
most appropriate
path.
Guidelines are:
Tooling
Hard
Tooling
Delivery of first article samples, 4 weeks (very
simple
parts) – 12
weeks
(normal
complexity)
– longer for
complex or
parts
requiring
ceramic core
tooling
Delivery of
production,
2 – 12 weeks
after First
Article
approval.
Highest tooling expense
Lowest
investment
casting
pattern cost
Hard tooling will have the longest life. Simple
tooling will
last for
hundreds of
thousands of
parts.
Complex
tooling with
slides and
cores will
wear over
time but can
generally be
refurbished.
This is not
normally
necessary
for many
years.
Yields the
best surface
finish and
most
consistent
dimensional
control.
Soft Tooling
Delivery of first article samples, 3 – 6 weeks
Delivery of production, 2 – 12 weeks after First
article approval
Soft tooling is
less costly than
Hard Tooling
Pattern cost is higher than Hard Tooling. This is
because the
tooling will
cycle slower due
to the poor
thermal
conductivity of
mold material
Life of soft tooling is limited. Life will depend
upon the
complexity of
part. The more
complex the
shorter the life
Surface finish and dimensional control is not as
good as Hard
Tooling
A single SLA (stereolithography) or Objet pattern
is generally
used to make the
tooling
Patterns made
from
individually
produced
patterns
Each casting
produced will
require one
pattern. This
method is
generally used
when small
quantities of
investment
castings are
required for
prototypes or
rapid production
of a few parts.
But it is
becoming more
and more popular
to use as the
fastest way to
produce
investment
castings where
design changes
or unknown
future
requirements
allow for higher
per piece
pricing since no
tooling expense
will be
incurred. Some
information
about suitable
investment
casting patterns
is in order. To
produce
investment
castings it is
necessary to
shell the
pattern. This
involves coating
the pattern with
a ceramic
material. After
shelling, the
pattern must be
removed from the
shell. This
produces a void
in the shell
which will be
the receptacle
for the molten
metal. When the
pattern is
removed from the
shell it must be
removed
completely and
without damaging
the shell.
Wax is a foundry
friendly pattern
material.
The wax is
removed from
shell by
heating. This is
generally done
in an autoclave
very quickly.
As the shell
heats up the wax
in immediate
contact with the
shell quickly
changes state
from solid to
liquid and is
absorbed into
the porous shell
thus allowing
room for the
balance of
pattern wax to
heat up, expand
and be drained.
Some of the RP,
rapid prototype,
patterns do not
melt and must be
burned out of
shell.
Unfortunately
some also expand
and can severely
crack the shell
if not hollow.
On thin edges it
is not possible
to hollow the
section and that
is where the
foundry’s
expertise is
needed to help
chose the most
appropriate
pattern for your
application.
3
Dimensional
Printers, MJM,
Multi-Jet
Modeling
ThermoJet RP,
rapid prototype,
patterns are the
best choice for
certain part
configurations
where thin
sections would
be a problem to
produce a
pattern suitable
for investment
casting, due to
problems
removing some
other types of
RP, rapid
prototyping,
patterns from
shell.
Surface finish
and dimensional
stability is
dependent upon
part
configuration
SLA, QuickCast
Stereolithography
patterns
Highest quality RP, rapid prototype, patterns
from dimensional
and surface
finish point of
view
SLS, CastForm
Selective Laser
Sintering
patterns
Surface finish
is rough, about
250 RMS.
Dimensionally of lower quality
than SLA patterns.
Objet
Highest quality
RP, rapid
prototype,
patterns from
dimensional and
surface finish
point of view.
Patterns must be
hollowed out.
Z-Corp
Investment
Casting Pattern
Material
Surface finish is the roughest of all RP rapid
prototype
patterns.
Least consistent
dimensional
stability of all
RP, rapid
prototype,
patterns;
Least costly of
all RP, rapid
prototype
patterns
The most important thing to remember is to get
the foundry
involved in your
design early to
allow the
foundry to give
advice on how to
make the part
friendlier for
investment
casting.
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