[IE 21] - 1.6 - Casting

Casting

Liquid material is introduced to a cavity or mold and permitted to solidify

Mold cavity

• Has the desired shape and size

• Has an allowance for shrinkage of solidifying metal

Melting process

Provides molten material at the proper temperature, in the desired quantity, with acceptable quality, at a reasonable cost

Pouring

Introduce the molten metal into the mold

Solidification process

Should be properly designed and controlled

Expendable-mold casting

Mold is used once to produce a single casting

San casting

• Most common casting process

• No size, shape, weight, complexity limit

• Low cost

• Almost any metal can be cast

• Tolerances and surface finish are porrer than other casting processes

• Slow production rate

Shell molding

• Common metals cast using this.

• Used to cast Cast Irons and casting alloys of aluminum and copper

Plaster mold casting

• Uses plaster, a slurry containing calcium sulfate (sometimes called gypsum)

• High dimensional accuracy

• Smooth surface finish

• Can produce thin sections

• Lower-temperature nonferrous metals only

• Long molding time

Ceramic mold casting

• Uses ceramic powder, a mixture of graded refractory fillers that are blended to a slurry consistency

• Intricate details, close tolerances, and smooth finish

• Mold materials is costly and not reusable

Investment casting

• Uses wax or plastic pattern

• Excellent surface finish

• High dimensional accuraciy

• Almost unlimited intricacy

• Costly patterns and molds

• Labor costs can be high

• Limited size

Multiple-use-mold casting

Mold is used multiple times to produce castings

Permanent-mold casting

• a.k.a. gravity die casting or hard-mold casting

• Die is commonly made of steel or iron

• Good surface finish

• Good dimensional accuracy

Die Casting/Pressure Die Casting

• Molten metal is forced into metal molds under pressures of several thousand pounds per square inch and helf under high pressure during solidification

• Extremely smooth surfaces

• Excellent dimensional accuracy

• Rapid production rate

• High initial die cost

• Limited to high-fluidity nonferrous metals

Centrifugal casting

• Inertial forces of rotation or spinning are used

• Cylindrical parts

True centrifugal casting

• Dry-sand, graphite, or metal mold is rotated

• Molten metal is flung to the surface of the mold as it is introruced

• Exterior profile is usually round

• Inner surface produced is always cylindrical

Semi-Centrifugal casting

• Produce solid castings

• Requires a code to produce hollow cavities

• Symmetrically shaped objects

• Mold is always vertical

Centrifuging

• Uses centrifugal action to force metal from a central pouring reservoir or sprue, through spoke-type runners, into separate mold cavities

• Relatively low rotational speeds

• Assist in the pouring of multiple-product invesment casting trees