Course Material on

Fundamentals of Manufacturing Processes

Faculty: Dr. B.Venkateshwarlu, Associate Professor,

School of Mechanical Engineering

VIT University, Vellore

Fundamentals of Manufacturing Processes (MEE 205)

MEE 205

Terminology:

Cast Product is also called as “ CASTING”

https://www.youtube.com/watch?v=l638qR0Y6YE

Step1: Preparation of Drag Box

Sprinkle dry facing Sand after placing the pattern

Step2: Preparation of Cope Box

Lecture 4

Fluidity: The physical property of a substance that enables it to flow.

Moulding Sand Composition

Ingredients of Moulding Sand:

• Silica grains (SiO2)

• Clay (as binder)

• Moisture (to activate clay and provide plasticity)

Refractory: Resistance to heat

Ex: Silica is a very good refractory material (1,713 °C)

It is the ability of the moulding material to resist the temperature of the liquid metal to be poured so that it does not get fused with the metal. The refractoriness of the Silica sand is highest.

Permeability tells us how well the generated gases can pass through the moulding sand

The moulding sand must be sufficiently porous to allow the dissolved gases, which are evolved when the metal freezes or moisture present or generated within the moulds to be removed freely when the moulds are poured. This property of sand is called porosity or permeability.

It is the important property of the moulding sand and it is defined as the sand particles must be capable of adhering to another body, then only the sand should be easily attach itself with the sides of the moulding box and give easy of lifting and turning the box when filled with the sand.

Green strength is the strength of sand in the wet state and is required for making possible to prepare and handle the mould.

• If the metal is poured into a green mould the sand adjacent to the metal dries and in the dry state it should have strength to resist erosion and the pressure of metal.

• The strength of the sand that has been dried is called dry strength

At the time of pouring the molten metal the mould must be able to withstand flow and pressure of the metal at high temperature otherwise the mould may enlarge, crack, get washed or break

Hot Strength

The sand adjacent to the metal is suddenly heated and undergoes expansion. If the mould wall is not dimensionally stable under rapid heating, cracks, buckling and flacking off sand may occur.

Thermal stability

3-D View

Ferrous (Cast Iron, steel)or non-ferrous like aluminium

Thermosetting resin binder

2.5-4.0%

175-370 0C

Coated with a heat resistant lubricant (Silicone) to facilitate removal

The heated pattern partially cures the mixture

Curing of shell for 1 - 3 min at 250 0C – 450 0C

(Backing material)

Figure: Shell Moulding Process

Figure: Shell Moulding Process

Advantages :

-High precision and accurate castings with smooth surface finish can be produced economically.

-complex parts having intricate shapes, and cleaning of casting is reduced or completely eliminated.

-size of casting is 10 - 13.5 kg and minimum wall thickness 2 - 2.5mm is possible.

Examples: Brake drum, bushing, cam/cam shaft, piston, piston rings, pinions, pipe bends, air compressor crank cases, etc.,

https://www.youtube.com/watch?v=Xar5r9Jm04g

https://www.youtube.com/watch?v=UrUsaGussfc

Animated Movie of Investment Casting Process

WAX or Plastic (polystyrene)

Binder: Water, Ethyl Silicate, etc.

WAX drains off

Temperature of 90-175 0C

Temperature of 650-1050 0C

Ex: Aluminium, Magnesium, Zinc and copper based alloys

Patterns also can be made of aluminium alloys, thermosetting plastics, Zinc alloys, etc.

Plaster of Paris + Water + Silica flour

Temperature of 120-2600C

Gears, Valves, Fittings, tools and Ornaments, etc.

(ZrSiO4)

(Al2O3)

Die Casting Process

Hot Chamber Die Casting process

Cold Chamber Die Casting Process

Centrifugal Casting Process

Rotational speed: 1000 rpm (250-3600 rpm)

• Core may or may not be used

• Mostly used for making hollow objects like pipes, tubes and bushes

The forces generated by the rotation of the mould ensure the distribution of molten material to all the regions of the casting

Semi centrifugal casting manufacture is a variation of true centrifugal casting and uses vertical axis with less rotational speeds.

The main difference is that in semi centrifugal casting the mold is filled completely with molten metal, which is supplied to the casting through a central sprue.

Castings manufactured by this process will possess rotational symmetry.

If a central bore is required in the casting, a dry sand core is best suited.