Types of Moulding Methods

Types of Moulding Methods in Metal Casting

Moulding is the process of creating a cavity (mould) that receives molten metal and shapes it into the desired casting. Based on the nature of the mould material, pattern usage, and production technique, moulding methods in metal casting are broadly classified into expendable mould and permanent mould processes. Each method is selected according to casting size, complexity, required surface finish, dimensional accuracy, and production rate.

1) Expendable Moulding Methods (Disposable Moulds)

These methods use moulds that are broken after each casting.

• Green Sand Moulding

Uses moist silica sand with clay and water.

• Most common and economical method

• Suitable for small to very large castings

• Moderate surface finish and accuracy

• Dry Sand Moulding

Similar to green sand but the mould is baked before pouring.

• Higher strength than green sand

• Better surface finish

• Used for heavier castings

• Loam Moulding

Uses a mixture of sand, clay, and organic materials applied over a brick structure.

• Suitable for very large symmetrical castings

• Time-consuming and skill-intensive

• Shell Moulding

A thin shell of resin-coated sand is formed over a heated metal pattern.

• Excellent surface finish and accuracy

• Ideal for small to medium precision parts

• Investment Casting (Lost Wax Process)

A wax pattern is coated with refractory material to form a ceramic mould.

• Very high precision and intricate shapes

• Excellent surface finish

• Used for aerospace and medical parts

• Lost Foam Casting (Expandable Pattern)

A foam pattern evaporates when molten metal is poured.

• No need for cores

• Complex geometries possible

• Good dimensional accuracy

• Plaster Mould Casting

Uses plaster of Paris as mould material.

• Very smooth surface finish

• Suitable for non-ferrous metals

• Not suitable for high temperatures

2) Permanent Moulding Methods (Reusable Moulds)

These methods use metal moulds that can be reused many times.

• Gravity Die Casting (Permanent Mould Casting)

Molten metal fills the mould under gravity.

• Good surface finish

• High production rate

• Used for aluminium and magnesium parts

• Pressure Die Casting

Molten metal is forced into the mould under high pressure.

Hot Chamber Die Casting

• For low melting point metals (Zn, Pb, Sn)

Cold Chamber Die Casting

• For aluminium and copper alloys

• Excellent finish and accuracy

• Very high production rate

• Centrifugal Casting

Mould rotates while pouring.

• Dense, defect-free cylindrical parts

• Used for pipes, liners, bushes

• Continuous Casting

Metal solidifies while continuously moving through a mould.

• Used for billets, blooms, slabs

• High productivity in steel plants

• Slush Casting

Metal solidifies at the mould wall and excess liquid is poured out.

• Produces hollow castings

• Decorative items, toys

Comparison of Moulding Methods

Selection Criteria for Moulding Method

• Size and complexity of casting

• Required dimensional accuracy

• Surface finish requirement

• Quantity of production

• Type of metal to be cast

• Cost considerations