Squeeze Casting

BY

HRISHIKESH D. GHEWADE(ROLL NO. 212215011)

M.Tech (Material Science and Engg.) 1st YearNIT TRICHY

Processing of MMC(Squeeze Casting)

05/02/2023 Squeeze casting 2

COMPOSITION OF MMC MMC’s are made by dispersing a reinforcing material into a metal matrix. The

reinforcing surface can be coated to prevent a chemical reaction with metal matrix.

For example: Carbon fibres are commonly used in aluminium matrix to synthesize

composite.

A matrix is usually a lighter metals such as Aluminium, Magnesium or Titanium and

provides a compliant support for the reinforcement.

The reinforcement can be a continuous or discontinuous.


MANUFACTURING PROCESSESA] Continuously Reinforced Composites: - Vacuum Hot Pressing (VHP)

B] Discontinuously Reinforced Composites: 1) Powder Metallurgy 2) Casting/ Liquid Metal Infiltration 3) Compocasting 4) Stir casting 5) Squeeze Casting or Pressure Infiltration


BACKGROUND• Before understanding the mechanism of any processing method, it is

necessary to take a prior knowledge of some concepts such as; 1) Interfaces (Wettability, Type of bonding, etc) 2) Preform Preparation 3) Infiltration Process


PREFORM PREPARATIONA. Adsorption and Wetting:

Good wettability is needed to generate a strong interface that will allow transfer and distribution of load from the matrix to the dispersed phase, without premature

Adsorption– It is a surface reaction which is dependent on concentration, temperature, and diffusivity. The greater the adsorption, the more the solute tends to lower the surface energy.

B. Surface treatment of the reinforcement The reinforcement surfaces are coated with suitable materials to

improve wettability and adhesion and also to prevent any adverse chemical reactions at elevated temperature.


Example - 1. Coatings of SiC on boron fibre for Al matrices. 2. B4C coating on boron fibres for Titanium matrices. C. Matrix Modification:

It is done by modifying the matrix alloy composition. Example- Alloying the Al matrix with Lithium promotes the

wetting of polycrystalline Al2O3 fibres. The Lithium is believed to react with alumina to form a lithium aluminate which is more readily wetted by aluminium.


INTRODUCTION TO SQUEEZE CASTING Squeeze casting is the combination of the casting and forging processes

that can be done with help of high pressure when it is applied during melt solidification.

It is a metal-forming process, which combines permanent mould casting with die forging into a single operation.

Referred by many names as “pressure infiltration”, “liquid metal forging”, ``extrusion casting”, “liquid pressing'', ``pressure crystallization”, ``squeeze forming”.

Employs low die filling velocity, with minimum turbulence and high applied pressure.


PRINCIPLE•Applying pressure on the solidification of molten metal could

change melting point of alloys which enhances the solidification rate.

•Moreover it refines the micro and macrostructure; it is helpful to minimize the gas and shrinkage porosities of the castings.


CLASSIFICATION

Squeeze Casting

Direct Squeeze Casting

Without metal movement

With metal movement

Indirect Squeeze Casting


DIRECT SQUEEZE CASTING The pressure for the infiltration of the prefabricated preforms is

applied directly to the melt. The die is thereby part of the mold, which simplifies the structure of

the tools substantially. Disadvantage: - The volume of the melt must be determined exactly - The appearance of oxidation products formed in the cast part during dosage


INDIRECT SQUEEZE CASTING The metal is injected into the die cavity by a small diameter piston

Pressure is transmitted from the hydraulic source to the metal in a

cavity through a runner system.

It is designed to combine the net shape advantage of highpressure die casting with the internal structural advantages of squeeze casting.


Squeeze Casting Infiltration process has the following steps:

• A preform of dispersed phase (particles, fibers) is placed into the lower fixed mold half.• A molten metal in a predetermined amount is poured into the lower

mold half.• The upper movable mold half (ram) moves downwards and forces the

liquid metal to infiltrate the preform.• The infiltrated material solidifies under the pressure.• The part is removed from the mold by means of the ejector pin.


List of variables and parameters Molten metal pouring temperature; Melt volume; Melt quality and quantity; Preform preheating temperature; Die temperature; Applied squeeze pressure; Pressurization rate; Pressure applied duration;


Theoretical background: Effect of pressure on solidification behaviour of alloy:• The application of pressure during solidification would be

expected to affect phase relationships in an alloy system. This may be deduced by considering the Clausius-Clapeyron equation,

where Tf is the equilibrium freezing temperature, Vl and Vs are the specific volumes of the liquid and solid, respectively, and ΔHf is the Latent heat of fusion.


• Substituting the appropriate thermodynamic equation for volume, the effect of pressure on freezing point may roughly be estimated asfollows:

• where P0, ΔHf and R are constants. Therefore, Tf should increase with increasing pressure.


SQUEEZE CASTING OF

ALUMINUM METAL MATRIX COMPOSITES


Among all the MMC’s Aluminum metal matrix composites are finding increased applications, because of their improved mechanical and tribological properties.

Matrix- Aluminum metal and Reinforcement- SiC Particles Parameters involved: 1) Squeeze Pressure: - Of the order of 100 MPa - Improves wettability and bonding force - Results in large undercooling and hence high nucleation rate- refinement change in structure. - A primary α (Al rich) phase seen as light dendritic areas and eutectic matrix of the α phase and silicon particles (darker areas)


- Role: 1) the decrease of grain size 2) Decreasing SDAS 3) Reduction of porosity 4) increase in heat transfer coefficient 5) preventing Al4C3 6) Microstructural refinement, 10% increase in tensile strength2) Casting (melt) / Preform preheat / Die temperature: - Best melt temperature is either 690°C or 660°C , at 630°C, the formation of very fine and uniform equiaxed grains. - SiC preform is preheated to 600°C- forms SiO2 layer - Die preheating temperature of 200°C-250°C, it shows increase in tensile strength and elongation.


3) Solidification Rate: - Very high - The relation between the grain size “d” and the cooling rate“R” is written as: Kwhere, K and d are constants. ‘a’ is factor which depends on type of composites. (0.34-0.39)


• Conclusions: - the grain size increased when the cooling rate decreased - The shorter the solidification time, the higher is the value of the property - The interface heat transfer coefficients were found to increase with the increase in applied pressure.

4) Reinforcement Particle Size:• When the particle size is smaller, the spacing between the particles is reduced.

The smaller particles will exert more constraint on grain growth during coolingand more restriction on plastic flow during deformation, which can also contribute to increase in the strength.

• Optimum reinforcement particle grain size of SiC in the range of 15-30 μm • The higher particle size which reduces the nucleation sites during the solidification and

a weaker the bond strength which becomes the crack initiation sites in the composites.


5) Porosity and Mechanical properties:• The applied pressure increases the volume fraction of the Al-rich α-phase, and

decreases in the size of the primary Al-rich dendrites.• High applied pressure finer microstructure increasing the freezing point

increases nucleation frequency finer grain size structure low or no porosity• Increase in tensile properties, hardness, flexural strength


CONCLUSIONS1. The optimum pressure used in the squeeze casting of Aluminium alloys and composites, which gives a better microstructural refinement and increase in the mechanical properties, is 100 MPa.2. The selection of the reinforcement particle size also influences the strength of the material in the squeeze casting process. The smaller the grain size the better the improvement in the properties.3. The suggested melt and die temperature during the squeeze casting of Aluminium alloys and composites are 600°C to 700°C and around 250°C respectively.4. There is a refinement in the microstructure with the combined effect of undercooling and a higher cooling rate, due to the high pressure level in the squeeze casting process.5. The mechanical properties are enriched for both the alloys and the composites when fabricated through the squeeze casting technique, under controlled process parameters.


ADVANTAGESElimination of porosity and shrinkage

100% casting yield

Attainment of greater part details

Good surface finish, good dimensional accuracy

High strength to weight ratio

Improved wear resistance, higher corrosion resistance, resistance to high temperature

Higher hardness

Improved fatigue and better creep strength


DISADVANTAGES

Costs are very high due to complex tooling.

No flexibility as tooling is dedicated to specific components

Process needs to be accurately control which slows the cycle time down and

increases process cost

High costs mean high production volumes are necessary to justify equipments

investment.


COMPARISON


REFERENCES 1. M.R. Ghomashchi, A. Vikhrov, “Squeeze casting: an overview”, Journal of

Materials Processing Technology 101 (2000) 1-92. M. Dhanashekara, V. S. Senthil Kumar, “Squeeze Casting of Aluminium Metal

Matrix Composites- An Overview”, 12th global congress on manufacturing and management, GCMM 2014, procedia Engineering 97 ( 2014 ) 412 – 420

3. Krishnan K. Chawla, “ Composite Materials- Science and Engineering”, Springer Publication

4. T.R. Vijayaram, S. Sulaiman, A.M.S. Hamouda , M.H.M. Ahmad, “∗ Fabrication of fiber reinforced metal matrix composites by squeeze casting technology”, Journal of Materials Processing Technology 178 (2006) 34–38


THANK YOU

Squeeze Casting

Engineering

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