net shape components spf

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

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Titanium Pane

made b SPF usin Horizon 94 A

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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.

net shape components spf

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