Chapter 11 Metal Casting Process

(True or False) In hot‐chamber die‐casting machines, molten metal is poured into an unheated chamber from an external melting container, and a piston is used to inject the metal under high pressure into the die cavity:

False

Which die casting machines usually have a higher production rate, cold-chamber or hot-chamber, and why?

Hot-chamber machines are faster because cold-chamber die casting machines require molten metal to be ladled into the chamber from an external source

Which one of the following casting metals is most important commercially:

cast iron

Which two of the following names are applied to processes in which a molten metal is poured into a heated lower die, and the upper die is closed to create the mold cavity only after solidification begins:

liquid‐metal forging rheocasting

(True or False)Semi‐solid metal casting is a family of net‐shape and near net‐shape processes performed on metal alloys at temperatures between the liquidus and solidus, so that the casting operation is performed on molten metal in which some dendrite formation has already occurred:

Correct! Dendrite formation would normally occur between the liquidus and solidus, but the mixture used in this process consists of solid metal globules in a liquid rather than the more typical dendritic solid shapes. This is achieved by forcefully stirring the slurry to prevent dendrite formation and instead encourage the spherical shapes.

What are some of the operations required in sand casting after the casting is removed from the mold?

The operations include (1) trimming, in which the sprues, runners, risers, and flash are removed, (2) core removal, (3) surface cleaning, (4) inspection, (5) repair if needed, (6) heat treatment, and (7) machining

Most commercial nonferrous casting metals are not alloys because the melting temperatures of alloys are higher:

False Most commercial nonferrous casting metals are alloys.

What is flash in die casting?

Flash is a thin portion of metal at the exterior of a casting that results from molten metal being squeezed into the spaces between the die halves of the mold at the parting line, or into the clearances around the cores and ejector pins.

Thixomolding is a semi‐solid metal casting process used for which metal

Magnesium

Silica sand has which one of the following chemical compositions

SiO2

What is the composition of green sand in the green-sand molding process?

The sand is composed of silica sand, clay, and water.

(True or False) Slush casting is a permanent‐mold process in which a hollow casting is formed by inverting the mold after partial freezing at the mold surface to drain the liquid metal in the center:

True

(True or False) Steel can be cast in permanent‐mold processes, but because of its high melting temperatures, the mold must be made of a refractory material:

True

(True or False)Unlike expendable molds, permanent molds do not collapse, so the mold must be opened before appreciable cooling contraction occurs in order to prevent cracks from developing in the casting:

True

Machining allowance refers to additional material left on the casting to machine surfaces or geometric features that cannot be achieved in the casting operation:

True

The fabrication cost of the mold in expendable mold processes is a component in the total cost to produce each casting because each casting requires its own mold, whereas in permanent mold casting processes, the mold cost is apportioned over the quantity of parts made throughout the life of the mold:

True

What is vacuum permanent-mold casting?

Vacuum permanent-mold casting is a form of low-pressure casting in which a vacuum is used to draw molten metal into the cavity.

Which three of the following metals would typically be used in die casting:

aluminum cast iron steel

Which three metals commonly cast in permanent mold casting:

aluminum, brass, steel

Compared to sand casting, shell molding has four features:

better dimensional accuracy, better surface finish on casting, easier flow of molten metal during pouring,more expensive metal pattern is required

Relative to the size of the cast part in sand casting, the volumetric size of the pattern is

bigger

Cupolas are furnaces used to melt which one of the following metals:

cast iron

Shell molding is best described by which one of the following:

casting process in which the mold is a thin shell of sand bonded by a thermosetting resin

Which four are advantages of die casting over sand casting:

closer tolerances higher melting‐temperature metals can be cast higher production rates

When splattering occurs during pouring, solid globules of metal can become entrapped in the casting; this defect is called which one of the following:

cold shot

An indirect fuel‐fired furnace is an alternative name for which one of the following furnace types:

crucible furnace

An advantage of a plaster mold is that it is permeable, thus allowing escape of gasses from the mold cavity:

false The plaster mold is not permeable, thus limiting escape of gases. This is a disadvantage.

Which one of the following casting processes are capable of the closest tolerances for parts of the same size and metal:

investment casting

Investment casting is also known by which one of the following names

lost wax process

Which three of the following are other names for the expanded‐polystyrene casting process:

lost‐foam process polystyrene‐foam molding vaporizing‐foam casting

A misrun is which one of the following defects in casting:

metal solidifies before filling the cavity

For which one of the following reasons is a green mold named:

moisture is contained in the mold

To make molds containing multiple cavities, the individual patterns are attached to a structure called

pattern tree

The mold in investment casting is made of which two of the following materials:

plaster, sand

Surface cleaning of the solidified casting is most important in which one of the following casting processes:

sand casting

Which one of the following casting processes is the most widely used:

sand casting

An irregularity in the surface of the sand casting caused by erosion of the sand during pouring is called which one of the following:

sand wash

Which one of the following products would not be an appropriate application for zinc casting:

structural beam

( true or false) The expanded‐polystyrene casting process uses a mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold:

true

Ceramic‐mold casting is similar to plaster‐mold casting, except that the mold is made of refractory ceramic materials that can withstand higher temperatures than plaster: True or false

true

Which one of the following is the name of the casting process in which molten metal is poured into a rotating mold to produce a tubular part:

true centrifugal casting

Low‐pressure casting and vacuum permanent‐mold casting are similar. Which one uses lower‐than‐atmospheric air pressure in the mold to draw the molten metal into the cavity:

vacuum permanent‐mold casting

In which of the following tube casting processes is the casting wall thicker at one end of the tube than at the other end:

vertical centrifugal casting

The power generated by a certain heating furnace is 200 kW and its thermal efficiency = 40%. The unit energy for melting and pouring for the casting metal = 800 J/g, and the total weight of the metal to be heated in the furnace = 50 kg. The time required to heat the metal for pouring is closest to which one of the following:

8 min

In plaster mold casting, the mold is made of which one of the following materials:(a) Al2O3(b) CaSO4‑H2O(c) SiC(d) SiO2

CaSO4‑H2O

Radial symmetry is not a requirement in which one of the centrifugal casting processes:

Centrifuge Casting

What is a chaplet?

Chaplets are metal supports of various designs used to hold the core in place in the sand mold