chapter 13 multiple-use-mold casting processes (part i) ein 3390 manufacturing processes summer a,...
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Chapter 13Chapter 13
Multiple-Use-Mold Multiple-Use-Mold Casting ProcessesCasting Processes
(Part I)(Part I)
EIN 3390 Manufacturing ProcessesEIN 3390 Manufacturing ProcessesSummer A, 2012Summer A, 2012
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Shape-Producing ProcessesShape-Producing Processes
Figure 11-1 The four materials processing families, with subgroups and typical processes.
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13.1 Introduction13.1 IntroductionIn expendable mold casting, a separate
mold is produced for each casting and has the following disadvantages:◦Low production rate◦Quality control issues, such as dimensional
and property variation due to Mold to be crated each time Variation in mold consistency Mold strength Mold moisture content Pattern removal
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13.1 Introduction13.1 IntroductionMultiple-use molds
Assets:◦Higher productivity ◦Good product quality
Liability:◦Metal molds are limited to low melting temperature nonferrous metals and alloys
◦Part size limitation◦Higher cost of dies or molds
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13.2 Permanent-Mold Casting13.2 Permanent-Mold CastingAlso known as gravity die castingMold materials:
◦Gray cast iron, alloy cast iron, steel, bronze, or graphite
Most molds are made in segments with hinges to allow rapid and accurate closing◦Molds are preheated to improve properties
Liquid metal flows through the mold cavity by gravity flow
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Permanent Mold CastingPermanent Mold CastingProcess can be repeated immediately
because the mold is still warm from the previous casting
Most frequently cast metals◦Aluminum, magnesium, zinc, lead, copper, and
their alloys◦If steel or iron is to be used, a graphite mold
must be used
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Advantages of Permanent-Mold Advantages of Permanent-Mold CastingCastingNear- net shapesLittle finish machiningReusable moldsGood surface finishConsistent dimensionsDirectional solidificationFast cooling rate to produce a strong
structureCore can be used to increase complexity
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Disadvantages of Permanent Disadvantages of Permanent Mold CastingMold Casting
Limited to lower melting temperature alloys
High mold costs◦Mold life is strongly tied to cost◦Mold life is dependent on the following factors:
Alloys being cast, especially melting temperature Mold material Pouring temperature Mold temperature Mold configuration
◦High production runs can validate high mold costsLimited mold complexity
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Low Pressure Permanent-Mold Low Pressure Permanent-Mold CastingCastingMolds are not permeable
◦Venting in Permanent Casting Slight crack between mold halves Very small vent holes to permit escape of trapped
air, but not passage of molten metalDesign feature affects mold life
◦Difference in section size through moldRemoval castings immediately after
solidification
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Permanent Mold CastingPermanent Mold Casting
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Low Pressure Permanent-Mold CastingLow Pressure Permanent-Mold Casting
Low pressure permanent-mold (LPPM) casting◦Mold is upside down and connected to a crucible that
contains the molten metal◦Pressure difference induces upward flow◦Metals are exceptionally clean because it is fed
directly into the mold◦Little or no turbulence during flow◦No risers, yields > 85%◦Mechanical properties are about 5% better than
those of conventional permanent-mold casting.Typical metals cast using low pressure process
◦Aluminum, magnesium, and copper
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Low-Pressure Permanent-Mold Low-Pressure Permanent-Mold CastingCasting
Figure 13-2 Schematic of the low-pressure permanent-mold process. (Courtesy of Amsted Industries, Chicago, IL.)
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Vacuum Permanent-Mold CastingVacuum Permanent-Mold CastingAtmospheric pressure in the chamber
forces the metal upward after the vacuum is drawn
Thin-walled castings can be madeExcellent surface qualityCleaner metals than low pressure
◦Lower dissolved gas contentBetter mechanical properties than low
pressure castingFinal castings range 0.2 to 5 kg and have
better mechanical properties than LPPM.
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Vacuum Permanent-Mold Vacuum Permanent-Mold CastingCasting
Figure 13-3 Schematic illustration of vacuum permanent-mold casting. Note the similarities to the low-pressure process.
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13.3 Die Casting13.3 Die CastingMolten metal is forced into the mold under
high pressureHeld under high pressure during
solidificationCastings can have fine sections and
complex detailsLong mold lifeTypical metals cast
◦Zinc, copper, magnesium, aluminum, and their alloys
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Advantages of Die CastingAdvantages of Die CastingHigh production ratesGood strengthIntricate shapesDimensional precisionExcellent surface qualitiesSmall-medium sized castings
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Disadvantages of Die CastingDisadvantages of Die CastingHigh cost for diesLess flexibility for productsLimited to small- to –medium-sized
partsMost for nonferrous metals and alloys
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Die Modifications and Die Life Die Modifications and Die Life Die complexity can be improved through
the use of◦Water cooled passages◦Moving pins to eject castings
Die life ◦Limited by erosion and usage temperature◦Surface cracking◦Heat checking◦Thermal fatigue
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Die Modifications and Die Life Die Modifications and Die Life Die Materials
◦Harden tool steels, since cast iron cannot withstand casting pressures
Vary Pressure on Molten Metal during casting◦Reduce turbulence and air entrapment by lower injection pressures, and followed by higher pressures after mold has been filled completely and metal starts to solidify.
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Die-Casting DiesDie-Casting Dies
Figure 13-4 Various types of die-casting dies. (Courtesy of American Die Casting Institute, Inc., Des Plaines, IL.)
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Basic Types of Die-CastingBasic Types of Die-CastingHot chamber castings
◦ Gooseneck chamber for molten metal◦ Plunger to control molten metal flow
Fast cycling timesNo handling or transfer of molten metalCan’t used for higher-melting-point metals
◦Aluminum tends to pick up some iron of casting equipments
Used with zinc, tin, and lead-based alloys
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Die Casting (Hot-Chamber)Die Casting (Hot-Chamber)
Figure 13-5 (Below) Principal components of a hot-chamber die-casting machine. (Adapted from Metals Handbook, 9th ed., Vol 15, p. 287, ASM International, Metals Park, OH.)
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Basic Types of Die CastingBasic Types of Die CastingCold-chamber machines
◦Used for materials not suitable for hot chamber machines
◦Separated furnace◦Drive measured quantity of molten metal into
unheated chamber by hydraulic plunger◦Maintain or increase pressure until solidification
done◦Typical materials
Aluminum, magnesium, copper, and high-aluminum zinc◦Longer operating cycle than hot-chamber◦High productivity
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Die Casting (Cold-Chamber)Die Casting (Cold-Chamber)
Figure 13-6 (Above) Principal components of a cold-chamber die-casting machine. (Adapted from Metals Handbook, 9th ed., Vol 15, p. 287, ASM International, Metals Park, OH.)
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Summary of Die CastingSummary of Die CastingDies fill so fast with metal, only little time for
the air in the runner and die to escapeMolds offer no permeability
◦Air can become trapped and cause defectsRisers are not used because of the high
pressures usedSand cores can’t be used due to high
pressures◦Cast-in inserts can be used
High production ratesLittle post casting finishing necessary
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Die CastingDie Casting
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Die Cast MaterialsDie Cast Materials