Energy Materials Testing Laboratory EVALUATION FROM

MoDEL FoR PowDER PRESSING AND DIE DESIGN, PART 2
Summary of Green Density, Fired Density and Firing Shrinkage*
Pressing Parameters Measured Density (%) Linear shrinkage (%)
Pressure (MPa) Length (mm) Green Fired Length Diameter
41.4 25.4 49.9 92.4 19.00 20.83
103.4 25.4 55.0 93.3 17.18 18.60
41.4 12.7 50.2 92.3 20.53 20.26
103.4 12.7 54.1 94.5 17.9 17.96
*In single-action, uniaxially pressed 94-wt% alumina powder tubes.
The FE compaction model was used
to simulate the exact same pressing
process used to form the nozzle
insert. The measured properties of
the 94-wt% alumina powder were
used along with a die wall friction
coefficient of 0.2 to complete the
simulation.
To complete a quantitative comparison
of the predicted and measured
density gradients in the uniaxially
pressed nozzle insert, spatial densities
were normalized to the density
of the entire powder compact. The
agreement between simulated and
measured densities is quite reasonable.
Some minor differences are evident
in pieces No. 1 and No. 5 at the top
and bottom of the part. The slight
over-estimation of the spatial density
may be related to heterogeneities
introduced during powder filling.
It also is possible that the coefficient
of friction between the die-wall
and the powder may be different
from the assumed value.
overall, results clearly confirm that
the FE model for simulating ceramic
powder compaction can be successfully
used to predict green density
distribution in a complex geometry
production part.
Applications in Ceramics
A model for ceramic powder compaction
has been developed, tested
and experimentally validated. This
model represents a powerful and
promising new tool that can be
applied for a better understanding
and control of the powder pressing
process.
The compaction modeling technology
developed can be used to troub
l e s h o o t e x i s t i n g p rocessing
problems, improve yields, reduce
waste and develop more efficient
manufacturing processes for problem
parts. Some improvements can
be realized with minor modifications
in die design and/or the pressing
process.
The compaction model also can be
used to improve tool and die design
by identifying and addressing design
problems in the initial stages of a
project. Instead of building a tool
that does not work, manufacturers
can use the compaction software to
identify potential problems and
refine die designs before any steel is
cut. Tooling can then be designed
with customer input, significantly
reducing design and prototyping
costs.
It is reasonable to anticipate that
the compaction software can help
ceramic component manufacturers
to expand current design limits,
which could lead to new products for
new markets.
A significant economic impact
could be realized by designing parts
that fire to net-shape without the
need for green machining and/or
hard grinding (i.e., diamond grinding)
after sintering.
In addition to simulating powder
pressing, the compaction model also
provides a means of relating powder
properties and characteristics to
pressing behavior.
Creating a good pressing powder is
the first step toward a robust manufacturing
process and the production
of reliable components.
The compaction model can provide a
systematic means of assessing and
understanding cause and effect
between powder characteristics and
powder compaction to optimize press
powder manufacturing. Similarly, the
compaction model also may provide
valuable information about ceramic
powders and their limitations in press-
ing.
Different powders have different
compaction responses, and not all
powders can be pressed to all geometries.
Pressable powders can be
formed into more complex geometry
powder compacts, but there are limitations
for harder-to-press powders.
Compaction simulations can be
used to assess and rank-order powders
in terms of pressability and to
establish use limits for certain powders.
Eventually, in combination with
readily measurable powder characteristics,
it may be possible to employ
FE compaction modeling with basic
powder data to guide the design and
development of more pressable
powders.
Overall, compaction modeling can
provide a more comprehensive
understanding of the compaction
process, identify critical process
parameters and define the process
control necessary for net-shape
pressing.
The application of compaction
modeling to develop more robust
pressing operations, design better
press tooling and to develop better
pressing powders will be a major
step toward developing more reliable,
efficient and cost-effective processes
for manufacturing ceramic
powder compacts. n
Acknowledgements
This work was supported by the U.S. DoE
under contract No. DE-AC04-94AL8500 to
Sandia National Labs, contract w-7405-
ENG-36 to Los Alamos National Lab and
by AMMPEC Inc. through a Southwest
R e g i o n D e p a r t m e n t o f Co m m e rce
Economic Development Agency Grant.
Sandia National Labs is a multi-program
laboratory operated by Sandia Corp., a
Lockheed Martin Co. for the U.S. DoE. Los
Alamos National Lab is an affirmative
ac tion/equal oppor tunity employer
operated by the University of California for
the U. S. DOE.
The authors thank Julie Bremser and
Martin Jones of Los Alamos National Lab,
and Mark Grazier and Arlo Fossum of Sandia
National Labs for their technical contributions
to this work. The authors also thank
Donald Ellerby of Sandia National Labs for
providing a critical review of this article.
The administrative support of Ronald E.
Barks to AACCMCI in support of the CRADA
is gratefully acknowledged.
46 The American Ceramic Society Bulletin, Vol. 80, No. 2