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Casting

11.3.1 Describe lost wax casting.

An ancient casting form that is still widely used today, used in sculpture, dentistry and jewellery. It is where a replica is made from the artists original by way of a mould produced using wax and plaster of paris.

11.3.2 Describe how lost wax cast products are made.

Consider preparation of the master pattern; injection of wax to create copy; creation of a wax tree to make a wide range of small parts from the same metal; covering wax with ceramic or plaster of Paris; removal of wax; and the addition of the final chosen material.

A nice flash animation from James Peniston Sculture

11.3.3 Explain how a range of products are made using lost wax casting.

Jewellery, dental implants, hip replacements and wind instrument keys.
  • Jewellery, dental implants, hip replacements and wind instrument keys are often intricate objects to produce.
  • They may also be unique, 'one of a kind', and thus lost wax casting
  • Can allow for replication of the items, small batch production.
  • Allows for hand made objects, such as jewellery, to be reproduced from the original

11.3.4 Describe high-pressure die casting.

Die casting is mainly used for low-melting alloys. Molten metal is forced into a mould under high pressure.

11.3.5 Describe how high-pressure die cast products are made.

Draw a diagram to include holding furnace, injector, gooseneck and die.

11.3.6 Explain how a range of products are made using high-pressure die casting.

Consider hip replacements, disk drive chassis and carburettors.

Hip replacements, disk drive chassis and carburettors all require a great amount of dimensional accuracy or in the case of disk drive chassis and carburettors thin walls can be produced accurately and without machining.

The process ...

  1. The Mould is prepared ... lubricated then closed
  2. The molten metal is squeezed (shot) into the mould under high pressure
  3. Pressure is maintained until the liquid solidifies
  4. The mould opens and the item (shot) and any flash or sprue are cleaned up

11.3.7 Outline two advantages and two disadvantages of high-pressure die casting.

Advantages: high accuracy, good surface finish, thin walls, and high rate of production.
  • High dimensional accuracy due to maintained pressure while cooling
  • Good surface finish due to the mould
  • Thin walls as the pressure squeezes into narrow flue
  • High rate of production as it can be automated
Disadvantages: high plant costs, high tooling costs, cannot be used for a wide range of alloys, and limitations on maximum size that can be cast.
  • High plant costs ... to buy the machines, staffing, running costs
  • High tooling costs ... to make the dies and lost production time when retooling
  • Cannot be used for a wide range of alloys ... as the properties of certain alloys are not suitable
  • Limitations on maximum size that can be cast ... the pressure needed would be great as would the cost of retooling

References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Page last modified on February 15, 2010, at 11:05 PM