a case study with my teammates for our college project ( casting course ) about the semi-solid metal for Faculty of engineering ain shams university mechanical department
4. What is the SSM ?!
• (SSM) is a short standard for the semi-solid
metal process
• Which is a manufacturing technique which
involves casting and forming operations .
• Discovered at MIT in 1971 During study of hot
tearing of steel during solidification
• regarded as an economical, high productivity
process for manufacturing a broad variety of
metal parts .
5. • Semi-solid metal casting (SSM) is “a near net shape ”
• “industrial manufacturing technique. the initial
production of the item is very close to the final (net)
shape, reducing the need for surface finishing “
• The process is used with non-ferrous metals,
such as aluminium, copper and magnesium.
• There are four processes: thixocasting, rheocasting,
thixomolding
6. Why SSM ?
• The conventional casting often
contains internal structural
defects that lead to poor
mechanical properties.
• to improve the mechanical
properties it is required to
modify the dendritic
microstructure of the alloys
8. Evolution to Non-dendritic Microstructure:
• Under Forced Convection
• Fragmentation of primary dendrites
by
• Root melting of secondary dendritic
arms
• Bending and shearing of secondary
denritic arms
• Bending and root melting of
secondary arms
• Fragments of primary dendrites grow
into globular grains under forced
convection
9. • Partial melting and Iso-thermal
holding
• Low temperature eutectic phase melts
in semi-solid range
• Highly stressed grain boundaries favours
wetting of grains with liquid
• Grain become globular to reduce
curvature and liquid-solid interface
energy
10. • Characteristics of Slurry
Sheared semi-solid slurry
shows apparent viscosity
similar to machine oil
11. • SSM Processing exploits
Solidification mechanism
in the solid-liquid range i.e.
nucleation and growth
mechanisms
Liquid
Solid
Liquid +
Solid
Composition, Time
Conventional
solidification
Semi-solid Processing
T
12.
13. • Solidification range
• Low melting point
phase/eutectic phase
• Temperature Sensitivity of solid
fraction
• Castability
• Potential for aging etc.
Temperature
FractionSolid
Processing Range
Alloy Characteristics:
18. Semi-solid Metal Processing Techniques
• Techniques for non-dendritic Feedstock:
• Mechanical Stirring
• Megnatohydrodynamic (MHD) Stirring
• Stress Induced and melt Activated (SIMA) Process
• Spray Forming
• Liquidus Casting
• Ultrasonic treatment
• Grain refienment etc.
19. • Mechanical Stirring
• Developed at MIT
• Stirring of liquid alloy while controlled
cooling in the semi-solid range using
auger, impeller or paddle
• Batch type or continuous process
• For Rheocasting andThixocasting
20. • Magneto hydrodynamic (MHD) Stirring
• Patented by Alumax Inc.
• Vigorous stirring by rotating magnetic field within the mould
• Normally for producing feedstock for thixocasting
• Disintegrated fine dendrites which convert to globular grains on partial
melting
• Most widely used process
21. • Stress Induced and Melt Activated (SIMA) Process
• Severe deformation of precursor results in residual stresses
• On heating recrystallization occurs
• On partial melting low melting point phase becomes liquid
• High residual stress favours wetting of grain boundaries
• Higher curvature and liquid-solid interface energy favours globular
grain morphology
• Longer holding time favours coarsening and agglomeration which
deteriorate semi-solidprocessability
22. • Liquid's Casting
• Pouring of melt at near-liqudus temperature
• Higher rate of Nucleation favouring fine grain size
• On partial melting fine grains transform to globular grains
• Grain Refinement
• Promote heterogeneous nucleation
• Finer grain size
• Grains transform to globular on partial melting
24. • Rheocasting:
• Non-dendritic ally slurry obtained from shearing while cooling from
liquid state
• Mechanical stirring
• MHD Stirring
• New Rheocasting (NRC)
26. • Thixomoulding:
• Simultaneous heating and shearing of solid feedstock in a
chamber by rotating barrel
• Designed for Mg alloy
• Controlled atmosphere
• Similar to injection moulding
27. • Rheomoulding:
• Vigorous Shearing of liquid alloy using
screw type drive while cooling
• Similar to Injection moulding
• Suitable even for immiscible alloy
formation and processing
• Twin Screw Rheomoulding (TSRM) process
is an upgradation
29. • Advantages:
• Energy efficient
• Production rate compete that for pressure die casting
• Smooth die filling with no air entrapment favouring
product soundness
• Lower processing temperature
• Lower Impact to the die
• Reduced solidification shrinkage
30. • Disadvantages:
• Relatively higher feedstock material cost
• Precise control of operating condition is required.
• Liquid segregation may occur as a result of non-
uniform heating
32. • Potential Applications:
• Replacement of permanent mould parts to eliminate machining and
finishing
• Pressure tight parts such as master brake cylinders, fuel rails, air
conditioner compressor housing etc.
• High strength parts such as engine mounts, tie rods etc.
• Wear resistant parts made from hypereutectic alloys such as
compressor piston, brake drums, gear shift levers etc.
• Forged parts requiring excessive tooling
34. Door Pillars for Audi
Control arms for Steering Fiat Engine bracket
35. • Process development
• Mechanism of formation of non-dendritic structure
• Alloy development
• Simulation studies of process
• Viable process for steel and Cast Iron
Future Developments