Casting and Moudings

CASTING AND MOULDING

Expendable Mould casting

Non-Expendable Mould Casting

Plastic Moulding Processes

Sand Casting:

-A mould is made from sand mixed with a binder material. Molten metal is poured into the sand mould. Once cool the the sand mould is removed leaving the cast.

-Produce up to 20 cast per hour.

-Suit for small or very large castings.

Plaster Mould Cast:

-Mould made from plaster of paris.

-Only low temperature melting and non- ferrous materials are used for castings.

-Process simular to Sand Casting.

Produces 1 - 10 units per hour.

-type of process used for small parts, very accurate

Shell Mould Casting:

-A cavity is formed by a hardned "shell" of sand and resin.

-Sand/Resin is heated and hardned to form a shell around desired pattern, Molten metal is then poured into the shell and left to cool, the shell is then removed leaving the cast metal.

-More precise than sand casting.

-Common metals used in this process: Iron, Aluminium, Magnesium and Copper.

Investment Casting:

-A wax pattern of a desired product is coated in a ceramic mixture then placed in heat to harden the ceramic and also melting the wax leaving a ceramic shell to make the metal casting.

-This process allows unlimited shapes and material types for casting.

Die Casting:

Forcing molten metal under high pressure into a steel mould cavity.

-Suitable for small to medium sized castings.

-Very good surface finish and dimensional accuracy + high production rates.

-Uses a hot or cold chamber machine.

Continuous Casting:

-Process were molten metal is solidified into basic shapes (Billet, bloom, Slab) for further rolling and forging in the mills.

-Continuous casting has been around since the 1950s.

-Since then continuous casting has achieved improved yeild, quality and productivity in aluminium and copper.

Centrifugal Casting:

-Molten metal is poured into the mould and solidified while the mould is rotating.

-Centrifugal force throw the liquid metal to the periphery.

-Used to cast small detailed products such as jewellery.

Permanent Casting:

-Reusable moulds made from metal.

-Metals used for this process are Aluminium, Magnesium and copper based alloys.​​​​​​ Iron and steel can also be cast using graphite moulds.

-Can be used a more than once but will eventually wear out.

-Good dimensional accuracy +high production rate.

Injection Moulding:

-Two mould halves are clamped together while granulates of raw material are fed from a hopper. A plunger forces materials through a pre-heated chamber were it is melted. Polymer is the injected into the mould. once cool the part is ejected and process repeats

Compression Moulding:

-Moulding material is preheated and placed into open mould cavity. Once the mould is closed heat and pressure is applied till the materials takes shape of the mould.

-Process used for complex parts large, and small and at low cost

Extrusion:

-Process simular to injections moulding.

-Plastic granulates are heated in a hopper and a screw thread forces the material through a die. and then cooled.

-Used to produce components that have constant cross sectional shapes such as pipes and curtail rails.

Blow moulding:

-Tube of plastic parisian is placed between two halves of a mould and heated before air is pumped through the parisian until it meets the edge of the mould it is then cooled and trimmed of any flash.

-used to manufacture bottles and containers with thin walls.

Transfer Moulding:

-Raw material is measured then heated until molten. A plumger force the molten plastic from the pot through a runner system into mould cavities. Mould remains closed as material is insurted then opened to release the part.

-Mould walls are heated to allow faster flow of materials through cavities