Multiple-Use-Mold Casting Processes Presented by: Amirhusain Momin ID:13103171

IntroductionIn expendable mold casting, a separate mold is produced for each castingLow production rate for expendable mold castingIf multiple-use molds are used, productivity can increaseMost multiple-use molds are made from metal, so most molds are limited to low melting temperature metals and alloys

Permanent-Mold CastingAlso known as gravity die castingMold can be made from a variety of different materialsGray cast iron, alloy cast iron, steel, bronze, or graphiteMost molds are made in segments with hinges to allow rapid and accurate closingMolds are preheated to improve propertiesLiquid metal flows through the mold cavity by gravity flow

Permanent Mold CastingProcess can be repeated immediately because the mold is still warm from the previous castingMost frequently cast metalsAluminum, magnesium, zinc, lead, copper, and their alloysIf steel or iron is to be used, a graphite mold must be used

The permanent mold casting process consists of the following steps:

Mold preparation- First, the mold is pre-heated to around 300-500F (150-260C) to allow better metal flow and reduce defects. Then, a ceramic coating is applied to the mold cavity surfaces to facilitate part removal and increase the mold lifetime.Mold assembly- The mold consists of at least two parts - the two mold halves and any cores used to form complex features. Such cores are typically made from iron or steel, but expendable sand cores are sometimes used. In this step, the cores are inserted and the mold halves are clamped together.Pouring- The molten metal is poured at a slow rate from a ladle into the mold through a sprue at the top of the mold. The metal flows through a runner system and enters the mold cavity.Cooling- The molten metal is allowed to cool and solidify in the mold.Mold opening- After the metal has solidified, the two mold halves are opened and the casting is removed.Trimming- During cooling, the metal in the runner system and sprue solidify attached to the casting. This excess material is now cut away.

Permanent Mold Casting

Advantages of Permanent-Mold CastingLittle finish machiningReusable moldsGood surface finishConsistent dimensionsDirectional solidification

Disadvantages of Permanent Mold CastingLimited to lower melting temperature alloysHigh mold costsHigh production runs can validate high mold costsMold life is strongly tied to cost

Vacuum Permanent-Mold CastingAtmospheric pressure in the chamber forces the metal upward after the vacuum is drawnThin-walled castings can be madeExcellent surface qualityCleaner metals than low pressureLower dissolved gas content

Vacuum Permanent-Mold Casting

High Pressure 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 castZinc, copper, magnesium, aluminum, and their alloys

Advantages of Die CastingHigh production ratesGood strengthDimensional precisionExcellent surface qualities

Disadvantages of Die CastingHigh initial cost.Limited to high-fluidity metals.

Die-Casting Dies

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