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8/6/2019 Net Shape Components SPF
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Net shape casting of ceramic
components for hot forming andSPF presses
By Ron Jones
Horizon Composites Ltd
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ComponentsHorizon use a net shape ceramic
manufacturing process for making
components for Hot Forming and SPF
presses
The components include:
Thermal shield around the press
Ceramic platens
Rapid ceramic tooling
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Advantages of the Horizon Process
In most conventional casting or pressing processes leadto high shrinkage when the ceramic component is fired inthe kiln. This can be as high as 25% for a slip cast
component. The designer could factor this into mouldgeometry if it were not for the fact that varying sectionthickness in s ceramic part leads to varying shrinkage sosometimes parts come out of the kiln with distortion.
The Horizon process generates shrinkage often lessthan 0.2% after firing and section thickness change doesnot matter
The Horizon process gives true net shaped componentswhich can also be produced in a reinforced form whichincreases toughness and hardness
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Contd The microstructure of the ceramic made by this
process is very different to that resulting fromother manufacturing technology. The porosity in
the ceramic is small and spherical which act as acrack stoppers so freeze cast ceramics havemuch better thermal shock resistance than anidentical composition made another way, inaddition the ceramic be can be reinforced.
Tooling used in the process can be madecheaply from fabricated sheet metal and rapidprototype patterns
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Thermal shock resistance is well illustrated in
casting of superalloys include Freeze Cast
expendables such as pouring cups andturbine blade cores
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Hollow Structures For thermal barriers and shields the most
effective components are hollow shell structures
filled with insulation. Traditionally hollow ceramic shell structures
have been made using slip casting but thisprocess has high shrinkage and many
geometries cannot be made this way Horizon use a rotational moulding process to
make hollow structures which are used asmodular units in furnace construction and otherthermal shielding such as around the hot press
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Thermal shields for hot presses
These refractory modules
fit together with dry joints
and form stablemechanical structure
If modules get damaged
they can be easily
removed and replaced
The modules have low
thermal mass so they
reduce energy
consumption
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Interlocking geometry of hollow blocks used
in thermal shielding on hot presses
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The modules can be used to construct
pre-heat kilns for SPF tooling
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Ancillary Parts for the Press
Complex parts with demanding
dimensional tolerances canalso be made without the
requirement for any machining
of the ceramic
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Ceramic SPF Tooling Low cost rapid prototype
ceramic tooling allows
parts to be made quicklyand tested. Tools are
typically good for 10 parts
Production tools can also
be produced by the
Horizon process whichare toughened and
hardened for more
rigorous use.
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Components made in Horizon diesCeramic Insert for Superplastic Forming Tool
Titanium Part Blown in Ceramic Insert
A
no
ed
ements to Uni
ersit
o
West o
En
and
or pro
idin
t
e p
oto
rap
s
Titanium Pane
made b SPF usin Horizon 94 A
umina Cerami
Die
Acknowledgements to British Aerospace, Manufacturing Technology & ToolingSalmesbury
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Sectional Tooling
It is possible to joinceramic sections to builda larger die
The advantage is that it is
not always necessary tokeep increasing plantcapacity to meet demand.
Illustrated opposite aretwo die halves being setfor firing then theassembly of the twohalves
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Complex geometry is achieved by casting only
Because ceramic dies made by a casting
process it is possible to create very complex die
geometry without the need for any machining
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Casting tools
Tools are cast using asuitable pattern which can
either be machined from
foam or tooling block or
using a rapid prototype
pattern such as an SLA
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A free standing ceramic die in use
on a 600 tonne SPF press
One additional advantage of ceramic dies is that they
do not lose heat as quickly as a metal die when the
press is opened for loading and part removal
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Die Coating Coatings can be infiltrated into the die surface to
add toughness and hardness. These coating
penetrates the porosity in the ceramic and isthere is no dimensional change after coating but
the coating increases the die strength by up to a
factor of 3.
This coating can be applied selectively so it ispossible to toughen a surface such as that on a
ceramic platen and improve platen life by
reducing the damage caused by metal tools.
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Ceramic Platens Horizon can produce ceramic blocks for use as
platens in Hot Forming and SPF presses.
The platens are cast net shape so expensivemachining is avoided
The top surface where elements are fitted canbe toughened so that this surface region is not
weakened by the element pockets or radiantinfra-red heaters can be incorporated near thesurface which are more efficient than sheathedelements.
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Case hardened surface of ceramic platen block
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New Development Horizon has been working on dies
manufactured from ceramic matrix
composites which have a high degree oftoughness and onto which can be applied
thick film heating elements so the die can
be self-heated to a pre-heat stage or to theforming temperature.