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Permanent Mold Casting

TECH 3421

Video

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Permanent Mold Casting Processes

  • Permanent Mold Casting
    • This is both a category and a specific process
  • Die Casting
  • Centrifugal Casting
  • Continuous Casting

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Permanent Mold Casting

  • Also known as gravity die casting
  • Molds are often cast iron, steel, bronze or graphite.
  • Molds made in halves with hinges or sliding action
  • Molds are preheated to allow material to flow
  • Used for aluminum, magnesium, zinc and others.
  • Grey iron can be cast in a graphite mold.
  • Suitable for small parts
  • Better surface finish than sand casting
  • Less complex castings
  • Expensive for low production

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Permanent Mold Casting - Variants

Bottom-Gated Permanent Mold

Tilt Pour Permanent Mold

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Permanent Mold Casting - Variants

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Low-Pressure Permanent Mold

Vacuum Casting

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Permanent Mold Casting

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Permanent Mold Casting (with cores)

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Advantages of Permanent Mold Casting

  • Near-net shapes
  • Little finish machining
  • Reusable molds
  • Good surface finish
  • Consistent dimensions
  • Directional solidification (chilling effect of the mold)

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Disadvantages of Permanent Mold Casting

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Higher mold costs (than sand casting)

Limited Complexity

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Die Casting

  • Sometimes called “Pressure Die Casting”
  • Molds are used multiple times
  • Metal is forced into die under pressure
  • Better for high production
  • Molds are usually made of metal
  • Complex shapes are possible
  • Castings have to have a relatively low melting temperature
    • Zinc
    • Aluminum
    • Magnesium

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Design Considerations For Die Casting

Draft

Avoid Undercuts

Avoid Cores

Holes can be problematic

Rounded Corners

  • Fillets
  • Rounds

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Examples of Die Cast Parts

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Die Casting Cavity and Runner System

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The finished part…

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Two Types of Die Casting Machines

Hot Chamber

  • Fast cycling times
  • No handling or transfer of molten metal
  • Used with zinc, tin, and lead-based alloys
  • Heated-manifold direct injection die casting
  • Molten zinc is forced through a heated manifold
  • Next through heated mini-nozzles directly into the die cavity
  • Eliminates the need for sprues, gates and runners

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Die Casting Hot Chamber

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Two Types of Die Casting Machines

Cold Chamber

  • Used for materials not suitable for hot chamber machines
  • Typical materials
  • Aluminum, magnesium, copper, and high-aluminum zinc
  • Longer operating cycle than hot-chamber
  • High productivity

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Cold Chamber Die Casting

Vertical and horizontal cold chamber arrangements

Vertical Cold-Chamber Machine

Horizontal Cold-Chamber Machine

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Die Casting (Cold Chamber)

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Centrifugal Casting

  • Uses centrifugal force to spread the metal over a spinning cavity.
  • Exterior of the part is usually round.
  • Can be horizontal or vertical
  • Impurities are forced toward the center

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Centrifugal Casting

Semi-Centrifugal casting

interior is formed by mold

True centrifugal casting

interior is formed by centrifugal force only

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Centrifugal Casting

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Rubber Mold & Centrifugal Rubber Mold Casting

Uses a spinning rubber mold to make small parts. Uses low temperature alloys.

Finish rivals die casting, but with lower cost tooling.

See: Conley casting supply catalog.pdf

Mold by Lucas Rivers

(Smooth-on Moldmax 60)

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Continuous Casting

Used to produce long lengths that are often rolled particular cross-section.

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Continuous Casting at Nucor Yamato

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Continuous Upward Casting

Outokumpu Upcasting Method

Uses water-cooled graphite dies

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Graphite or charcoal is used to deoxidize the melt

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Tesla’s Giga Press