Manufacturing Technology

Manufacturing Technology

1. Moulds

   • Open Moulds
   • Closed Moulds
     • Grating System: Channel, or network of channels, by which the molten metal flows into the cavity from the outside world.
       • Downsprue/Sprue through which metal enters a runner that leads to the main cavity.
         • At the top of sprue, a pouring cup is used to minimise splash and turbulence.
     • If shrinkage is significant, a riser is connected to the main cavity.
       • Riser: reservoir in the mould that serves as a source of liquid metal fore the casting to compensate for shrinkage during solidification.
         • Must be designed to freeze after the main casting in order to satisfy its function.
     • Air that previously occupied the cavity as well as hot gases formed by reactions of the molten metal, must be evacuated so that the metal with completely fill the empty space.
       • In sand casting the natural porosity of the mould permits the air and gases to escape through the walls of the cavity.
       • In permanent metal moulds small vent holes are drilled into the mould or machined into the parting line to permit air and gas removal.
   • Permanent Moulds
   • Expendable Moulds
   • Cavity in the mould provides the external surfaces of the part. A casting may have internal surfaces made from a core in the cavity.
     • In sand casting these are generally made from sand but metals, plaster, ceramics etc. can also be used.
     • Mould cavity formed by means of a pattern made from wood, metal, plastic or other material.
       • Sand casting - sand is packed around the pattern. Half in cope, half in drag.
         • Sand is moist and contains a binder to maintain shape.
       • Pattern oversized to allow for shrinkage of metal.

2. Sand Casting

   • Typical mixture of water and bonding clay is: 90% sand, 3% water, 7% clay.

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