IE 21 - Casting

• Solidification Process

  • various ways of transforming molten parts into their solidified state which will be used further in various manufacturing operations
• Solidification Process

  • Casting of Metals
  • Glassworking
  • Processing of polymers and PMCs
• Casting is a process which involves

  1. Pouring molten metal into a mold patterned after the part to be manufactured
  2. Allowing it to cool
  3. Removing the metal from the mold
• The term casting also applies to the part made in the process.
• Casting

  • usually done in the foundry
• Foundry

  • factory equipped for making molds, melting and handling molten metal, performing the casting process, and cleaning the finished casting.
• Foundrymen

  • this is what the workers who perform casting are called
• Mold

  • contains cavity whose geometry determines part shape
  • are made of a variety of materials, including sand, plaster, ceramic, and metal
• Actual size and shape of mold cavity must be slightly oversized to allow for shrinkage of metal during solidification and cooling.
• Expendable Molds

  • they are made of sand, plaster, ceramics, and similar refractory materials.
  • mixed with binders/bonding agents
  • after the casting has solidified, the mold is broken up to remove the casting
• Binders / Bonding agents

  • used to provide cohesiveness and structural stability.
• expendable

  • meant to be broken to get the product inside.
• Permanent molds

  • they are made of metals which maintain their strength at high temperatures
  • they can be used repeatedly due to their strength.
• Permanent Molds

  • they are designed to easily get the casting.
  • since they are made from metals, they provide better heat conductivity to the process.
• Composite molds

  • They are made of two or more different materials; such as sand, graphite, and metals.
  • Improve mold strength, control cooling rates, and optimize process economics.
• Composite molds

  • some materials require these due to their complexity
• Types of Mold

  • Expendable Molds
  • Permanent Molds
  • Composite Molds
• Types of Casting Processes

  • Sand Casting
  • Shell Mold Casting
  • Investment Casting
• Sand Casting

  • It is the traditional method of casting, making it to be the most prevalent even up to this day.
  • It is also added with binders such as clays, zircon, olivine, etc.
• Sand Casting

  • Most of the molding processes use Silica sand (SiO2) as the mold material because it resists high temperatures.
• Mulling machines

  • used to uniformly and thoroughly mull (mix) sand with additives
• TWO GENERAL TYPES OF SAND:

  • Naturally bonded – bank sand
  • Synthetic – lake sand
• Factors to Consider in Selecting a Proper Sand Model

  • Surface Finish (fine grains form smooth mold surface)
  • Good Permeability (allows steam and gases to escape)
  • Good collapsibility (allows shrinking while cooling)
• Classification of Mold in Sand Casting

  • Open Molds
  • Closed Molds
• Open mold

  • simply a container in the shape of the desired part
• Closed mold

  • mold geometry is more complex and requires a gating system (passageway) leading into the cavity
• Types of Sand Molds based on sand type and production

  method

  • Cold-box
  • Green-sand
  • No-bake molds
• Cold-box

  • organic/inorganic binders are blended for better dimensional accuracy.
  • more expensive than green sand.
• Green-sand

  • Sand + Clay + Water
  • ‘green’ – sand is moist
  • Least expensive of making molds
• No-bake molds

  • Synthetic liquid resin mixed with sand
  • Hardens at room temperature
• Parts of a Sand Mold (Part 1)

  • Flask
  • Cope
  • Drag
  • Core
  • Core Print
  • Mold Cavity
  • Riser
• Parts of a Sand Mold (Part 2)

  • Gating System
  • Pouring Cup
  • Sprue
  • Runners
  • Parting Line/Surface
  • Draft
  • Core Box
• Flask

  • the box containing the mold
• Cope - the top half of any two-part mold
• Drag

  • the bottom half of any two-part mold
  • additional part are called cheeks
• Core

  • A shape inserted into the mold to form internal cavities or lettering on surface of casting
• Core Print

  • a region used to support the core
• Mold Cavity

  • The hollow mold area in which metal solidifies into the part
• Riser

  • An extra cavity that stores and supply additional metal to the casting as it shrinks during solidification (blind riser and open riser).
• Gating System

  • Channels used to deliver metal into the mold cavity