thixocasting or semi solid metal casting detail, process etc..

1. Thixocasting or Semi
Solid Metal Casting
contents by: CB.EN.P2MFG15006 : Ilyas Hussain
CB.EN.P2MFG15007 : Jithin Jose

2. Thixocasting
 Thixo is a general term used to describe the near-net
shape forming process from a partially melted non
dendrite alloy within a metal die.
 Thixotropy- viscosity decreases with time due to
constant agitation or strain.
 If component shaping is performed in a close die it is
called thixocasting.
 If component shaping is performed in an open die it
is called thixoforming.

4. process
 Thixocasting consists of three separate stages:
1. The production of a pre-cast billet having special
globular microstructure.
2. The re-heating of these billets to the semi solid
casting temperature.
3. Casting of component by pressing these billets to
die cavity.

5. Production of billet
 Non-dendritic billets of A356.2 aluminum alloy were
produced in the laboratory to manufacture SSM
components.
 Around 20 kg A356.2 aluminum alloy ingots were
loaded into a furnace and melted at 850 °C.
 Once the metal reached molten stage, the grain
refiner of Ti-B was added at 0.1% of the total metal
being melted, and the modifier of aluminum-
strontium of 0.06 % of the total metal being melted
was added to the molten metal and allowed to soak
for 10 min.

7.  Then, around 1.5 kg molten metal was transferred
into a crucible at about 750 °C, and when the
temperature reached 620 °C, the metal was poured
into the preheated metal mould kept inside the
electromagnetic stirrer.
 The electromagnetic stirrer was operated at 350A, 50
Hz. Once the metal temperature reached 610 °C in
metal mould, the water supply for the metal mould
was switched on and immediately allowed to pass
through the cooling channels to quench the metal in
the metal mould.
 The static mould billets were 230mm in length and
75 mm in diameter.

8. Metallic mould Electromagnetic stirrer

9. process
In Thixocasting, a solid billet with a globular grain
structure is prepared by stirring the melt first
while the billet is being cast, and then supplied to
the die caster.
This billet is then reheated to the semi-solid
temperature (between the solidus and liquidus
temperatures of the alloy) by the die caster, using
an induction furnace.
It is then placed in a shot sleeve and injected into
the die cast machine.
Since the melt is partly solidified, proper thermal
control of the die is essential to ensure proper
filling of the die cavity.

10. Dendritic microstructure Non dendritic microstructure

11.  Casting of non-dendritic billets using electromagnetic
stirring depends on many parameters, such as the
stirring intensity, excitation frequency and cooling
rate.
 A minimum shear rate should be produced so that
dendrites can be detached from their roots.
 The position of the stirrer in the mould is also very
important.

12.  Subsequent to the production of non-dendritic
microstructure billets, the process of re-heating of
the billet to the desired semisolid temperature is also
a challenging task.
 Induction heating is generally used to reheat the
billets in semisolid state.
 Major objective is to minimize non-uniformity in
temperature distribution.
 All these parameters affect the overall solidification
process which will determine the final
microstructure.

13. advantages
 Energy efficiency: metal is not being held in the liquid
state over long periods of time.
 Production rates are similar to pressure die casting or
better.
 Smooth filling of the die with no air entrapment and low
shrinkage porosity gives parts of high integrity (including
thin-walled sections) and allows application of the
process to higher-strength heat-treatable alloys.

14.  Lower processing temperatures reduce the thermal
shock on the die, promoting die life and allowing the
use of non-traditional die materials.
 Fine, uniform microstructures give enhanced
properties.
 Reduced solidification shrinkage gives dimensions
closer to near net shape and justifies the elimination
of machining steps.
 Surface quality is suitable for plating.

15.  Thixocasting has quite a low yield strength, high
fluidity, low forming load and low surface roughness.
 Especially in the thixocasting process, a complex
geometry product can be obtained by only one step
forming.
 This technology has been widely applied in
nonferrous metal forming and satisfactory results
were derived, but not with ferrous metal.

16. disadvantages
 The cost of raw material for thixoforming can be high
and the number of suppliers small.
 Process knowledge and experience has to be
continuously built up in order to facilitate application
of the process to new components.
 Personnel requires a higher level of training and skill
than with more traditional processes.
 Temperature control: the solid fraction and viscosity
in the semi-solid state are very dependent on
temperature.

17. applications
 Semi-solid processing is ideally suited for the
production of large volume die casting components,
including light weight, high strength components for
automobiles.
 For aluminum alloys typical parts include engine
suspension mounts, air manifold sensor harness,
engine blocks and oil pump filter housing.
 For magnesium alloys, semi-solid casting is typically
used to produce extremely thin walled castings, such
as computer and camera bodies. Because of this the
process can be applied to rapid prototyping needs
and mass production.

18. applications
 Automotive wheel.
 Antilock brake valve.
 Disc brake caliper.
 Engine piston.

19. Anti lock brake valve Disc brake caliper

20. Thank you