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Advanced metal formingAdvanced metal formingprocessesprocesses
Introduction/Objectives
Superplastic forming
Pressing and sintering
Isostatic pressing
Subjects of interest
Chapter 8
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This chapter aims to provide additional information on
several techniques of metal forming processes other than
those conventional process already mentioned in previous
chapters.
The requirements for the process selection will be added,
which are based on advantages and disadvantages of each
type of non-conventional metal forming processes.
ObjectivesObjectives
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Advanced techniques for metal forming are listed below;
IntroductionIntroduction
1) Superplastic forming
2) Pressing and sintering
3) Isostatic pressing (hot and cold)
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SuperplasticSuperplastic formingforming The term superplasticityis used to
describe materials that can be formed to
high strains without the formation ofunstable tensile necks.
Require controlled conditions of
appropriate temperature and strain
rate, by using low force. Produce complex shapes (3D) with
essentially constant section thickness.
Good surface finishes.
Poor creep due to small grain size.
Machines and dies are costly.Superplastic forming
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Female forming Female drape forming
Graphite coated blankput
into heated hydraulic press.
Air pressure forces sheet
into close contact with mould.
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Graphite-coated blank clampedovertraycontaining heated
male mould.
Air pressure forces metal into
close contact with mould.Tapany Udomphol
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Plug-assisted snap back male forming
Graphite-coated blankputinto heated press.
Blank formed into a bubble.
Male mould pressed into
bubble.
Air pressure forces metal
into close contact with mould.
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Pressing and sinteringPressing and sintering Powderis pressed in closed dies to form a green compact
which is then sintered at elevated temperature.
Produce 3D solid shapes for mainly metals and ceramics.
Near net shape process 100% material utilization. Automated machinery and dies are relatively costly.
Sintering Operation
Sequence of operations for production of cylindrical bearing
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Sintering of a powder compact
Sinteringis the "welding" together of separatepowder particles into a single solid material,
Takes place below the melting point of the
material, but at a temperature sufficiently high to
allow an acceptable rate of diffusion to occur.
Sintered products
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IsostaticIsostatic
pressingpressing
Powder is placed within a deformable container
and subjected to hydrostatic pressure.
Produce 3D bulk solid shapes for metals and
ceramics.
Allows simultaneous densification of metal
powder products have relatively low porosity.
Distortion is possible in high aspect ratiocomponents
Near net shape process100% material
utilization.
High operating cost.
Hot isostatic pressing (HIP).
process
HIP products
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Hot Isostatic Pressing (HIP)
Components are loaded
into furnace, which is placedinto pressure vessel.
Temperature and pressure
are raise simultaneously and
held. Coolingis carried out as
the gas is released (clean
and recycled) and the furnace
is removed from the pressurevessel.
Components are removed
from the furnace.
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Cold Isostatic Pressing (CIP)
Powderis sealed in a flexible
mould (or bag), of for example
polyurethane and then subjected to
a uniform hydrostatic pressure.
CIP graphite blocks
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Edwards, L. and Endean, M., Manufacturing with materials,
1990, Butterworth Heinemann, ISBN 0-7506-2754-9.
www.designinsite.dk/ htmsider/pb0278.htm
www.twi.co.uk/j32k/ getFile/ceramics_hip.html
http://www.sintec-keramik.com/sintec-en/hip-products.html www.thrive-metal.com/ product2.html
www.sv.vt.edu/.../ diffusion/apps/sinter.html
www.sti-us.net/ newdesign.htm
ReferencesReferences
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