Transcript RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYSA NEW TECHNOLOGY FOR MANUFCTURING AUTOMOTIVE AND AEROSPACE COMPONENTS Presented at the CSIR Research & Innovation Conference Unit: Metal.

RHEO-PROCESSING OF SEMI-SOLID METAL ALLOYSA NEW TECHNOLOGY FOR MANUFCTURING
AUTOMOTIVE AND AEROSPACE COMPONENTS
Presented at the CSIR Research & Innovation Conference
Unit: Metal & Metal Processes
L Ivanchev, D Wilkins, S Govender, W Du Preez, R Bean
Alloys and Processing
Date: 27.February, 2006
THE EQUIPMENT
Machine for rheo casting of metal alloys
by controlled cooling and induction stirring
from liquid to semi solid state have been
designed. The machine has been tested for processing of
aluminium alloy A356 and continuous delivery of mush
billets 72 mm diameter and 200 mm length.
These dimensions are not the limits of the process
and billets up to 15.5 kg were successfully treated.
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THE PROCESS
Molten metal at temperature close to the liquidus is pored
into stainless steel cups. They are moved in vertical
direction upwards and stepwise through three
conditioning units.
Each conditioning unit consists of an AC induction coil and few
air-cooling coils.
The induced electromagnetic field, supplied by the
induction coil, and the air blown from the air-cooling system
simultaneously tread the metal to the desired semi solid
temperature and structure.
The process was optimized to produce semi-solid billets
at a production rate of one billet per minute.
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THIXO
LIQUID
RHEO
•CASTING
Known since 3000 BC
Liquidus temperature
Globular structure
formation
•SEMI-SOLID METAL
CASTING/FORMING
SEMI-SOLID
Known since 1973 AD
Solidus temperature
•HOT FORMING
Known since 3500 BC
SOLID
•COLD FORMING
Known since 4000 BC
Ambient temperature
Fig.1. The metal forming processes places in a “Time- Temperature”
diagram
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(a) Dendrite structure
(b) Globular structure
Fig.2. Typical microstructure of an Al-7%Si alloy after:
(a) liquid casting and (b) semi-solid casting
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Fig.3. Plastic behavior
of an Al-7%Si alloy
treated to semi-solid
state-globular structure
and semi-solid
temperature, during
the technological
“kitchen knife” test.
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Thixocasting
(a) (SSM feedstock manufacturing
(b) Thixo casting of the feed-stock into a component
Fig.4. The two steps of thixo route of SSM casting method
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Rheocasting
Transfer
Cool
and
stir
Liquid Metal
Semi-solid metal with
globular grain structure
High Pressure Die Casting
Fig.5. Diagram of the one-step Rheo route of SSM casting method
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Fig.6. Assemblage of the experimental version of
CSIR Semi Solid Metal slurry maker
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Fig.7. Assemblage of the semi-industrial version of CSIR Rheo Casting machine:
the induction generator, the slurry maker, a 6-axis robot and the cup conditioning
unit are visible.
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Fig. 8. The three
conditioning units slurry
maker.
Each unit consists of an
induction coil and an air
spraying coil.
The induction coils provide
induced magnetic field into
the liguid metal to modify the
metal structure from
dendrite to globular.
The air spraying coil reduce
the metal temperature form
the liquid to the semi-solid
value of the particular alloy.
A cup full with liquid metal is
at the bottom waiting to be
up-wards processed.
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Fig.9. A ceramic lead above
the top coil of the slurry maker.
The three thermocouples
coming out of the lead are for
controlling the final
temperatures of metal at the
top-, the middle and the bottom
positions of the cup.
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Fig.11. A cup assembled with an aluminium consumable
washer as a bottom lead of the cup
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Fig.12. A cup, on the right, and an ejected billet of Al-7%Si alloy, on the left
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Fig.17. A rheo-processed and water quenched 15.5 kg billet,
122 mm diameter and 480 mm length. The alloy is A356,
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100 μm
100 μm
(a) Top surface
(b) Bottom centre
Fig.19. Microstructure at two positions of the 15.5 kg billet
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300 μm
(a) Top surface
(d) Top centre
(b) Middle surface
(e) Middle centre
(c) Bottom surface
(f) Bottom centre
Fig.18. Microstructure homogeneity in 6 positions of a 15.5 kg billet
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The main technological advantages of the SSM forming process are as
follows:
• Better mechanical properties, for example elongation
• Low gas porosity due to laminar filling and good airing
• Allows for casting of wide range of alloys inclusive of high strength wrought alloys.
• Production of thin walled components
• Longer life of the dies
• Joining by LASER, MIG or TIG welding possible
• Heat treatment from T0 - T7 possible
• Near net-shape parts production
• Excellent surface finishing
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APPLICATIONS OF SSM TECHNOLOGY
IN AUTOMOTIVE INDUSTRY
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•BRAKE CALIPERS
•ENGINE MOUNTS
•CLUTCH CYLINDERS
•PULEYS
•SUSPENSION ARMS
•ROCKER ARMS
•WHEELS
•BELT COVERS
•PISTONS
•MOTOR HOUSINGS
•KNUCKELS
•SPACE FRAMES
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The characteristics
of the A356 castings achieved in this work are:
Grain size: less than 85 m
Shape factor: less than 1.52
Mechanical properties in “T6” condition:
Yield Stress: 286 MPa,
Ultimate Tensile Strength: 334 MPa,
Elongation: 6.2 %
Maximum temperature variation in a single billet is 4C
Production rate: one billet per minute.
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THE PRESENT STATUS OF SSM TECHNOLOGY
Light Metal Components Market:
The total SSM market in North America is estimated to grow from 0.6
million metric tons/year in 2002 to 2.4 million metric tons in 2012, or
400%.
Structural castings: 20% in 2002 and 40% in 2012 growth / year;
High integrity castings: 10% in 2002 and 40% in 2012 growth / year;
Increasing Demand for Rheo Casting Technologies.
Number of Rheo Processes Reported:
1996 – 1
1998 – 0
2000 – 3
2002 – 5
2004 – 18 ( including CSIR process)
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Conclusions
•
The general world trend is a shift to rheocasting processes.
•
Increased interest from automotive and aero space industry to the
CSIR technology.
•
Although there are several new rheocasting processes, only one
process and equipment is currently commercially available.
•
We have a window of opportunity to enter world market in order
to compete with the international consortiums.
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