Permanent Mold Casting

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Permanent Mold Casting

• General Manufacturing Processes Engr.-20.2710
• Instructor - Sam Chiappone

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Multiple Use Mold

• Advantages
• Mold is reusable
• Generally, a good surface finish is obtained
• Dimensional accuracy can be as good as /- .003
• Control of mold temperatures

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Multiple Use Mold

• Disadvantages
• Majority of molds use low-melt alloys
• Mold costs can be high
• Mold life varies
• Temperature of alloy being poured
• Mold material
• Mold temperature
• Thermal shock
• Mold configuration

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Permanent Mold Casting (Gravity)

• The tool
• Molds are machined from tool steels and can have
  metal retractable cores
• The Process
• Molds are pre-heated
• Molten metal is poured into the molds and enters
  the mold cavity through the gate under gravity
  feed. After solidification.mold is opened and
  part removed

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Permanent Mold Casting

• Metals
• Aluminum, Zinc, Magnesium, Copper,and Brass
  Alloys
• Tolerances
• /- .012 first inch (add .002 per inch)
• Wall section .125
• Normal Minimum Section Thickness
• Aluminum.100" for small areas, up to 3/16" or
  more for large areas.
• Copper Base .060"
• Ferrous 3/16" for small areas, 1/4" normal.

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Advantages

• Generally the same as all other multiple use
  moldsand mold life is about 25,000 cycles

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Disadvantages

• Some limitations in complexity of mold and fine
  section detail may be limited

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Pouring Process
Figure 13-19 Automatic pouring of molds on a
conveyor line. (Courtesy of Roberts Sinto
Corporation, Lansing, MI.)
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Die Casting

• The Process
• Molten metal is forced into the die cavity under
  pressure. The metal is kept under pressure until
  it solidifies. Pressure ranges are 1,500 p.s.i.
  to 25,000 p.s.i.

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Process Steps

• Lubrication of dies
• Closing and locking of dies
• Molten metal is forced into the die cavity
• Held under pressure until it solidifies
• Die opens
• Casting is ejected

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Process Parameters

• Normal Minimum Section Thickness
• Al .03" Small Parts .06" Medium Parts
• Mg .03" Small Parts .045" Medium Parts
• Zinc .025" Small Parts .040" Medium Parts
• Tolerances
• Al and Mg .002"/in.
• Zinc .0015"/in.
• Brass .005"/in.
• Metals Aluminum, Zinc, Magnesium, and Brass

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Die Casting
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Die Casting
Figure 13-4 Various types of die-casting dies.
(Courtesy of American Die Casting Institute,
Inc., Des Plaines, IL.)
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Machines

• Hot Chamber
• 15 cycles per minute
• Direct transfer of molten metal into die cavity
• Used primarily with zinc and zinc alloys
• Cold Chamber
• Higher temperature alloys (aluminum and
  magnesium)
• Metal is melted in a separate furnace and
  transported to the machine
• Measured quantity of metal is forced into the
  mold by a hydraulic or mechanical plunger (can be
  a double plunger system for productivity)

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Advantages

• Fine section detail (.003)
• Excellent dimensional accuracy (/- .002)
• High production rates
• Excellent surface finish
• Control of process temperatures
• Extended mold life
• Limited part defects

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Disadvantages

• Part size (up to 75 lbs.)
• Limited to low melt alloys
• Initial tooling costs are high

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Process Selection and Cost

• Each casting process has advantages and
  disadvantages
• Typical requirements
• Size, complexity, dimensional precision, surface
  finish, quantity, rate of production
• Costs for materials (dies, equipment, and metal)

Figure 13-20 Typical unit cost of castings
comparing sand casting and die casting. Note how
the large cost of a die-casting die diminishes as
it is spread over a larger quantity of parts.
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Process Selection and Cost