Formningsteknik - assignment 2 (review+multiple choice quiz)

Name the two basic categories of casting processes

Expendable and permanent mold

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 spaces between the die halves of the mold at the parting line, or into the clearances around the cores and ejector pins

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 the external source. Ladling takes more time than injecting the molten metal into the die as in the hot-chamber operation.

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

Trimming, core removal, surface cleaning, inspection, repair if needed, heat treatment and machining.

What is the difference between vacuum permanent-mold casting and vacuum molding?

Vacuum permanent-mold casting is a form of low pressure casting in which a vacuum is used to draw molten metal into the cavity. Vacuum molding is sand casting in which the sand mold hold together by the vacuum pressure metals used in die casting.

What is a chaplet?

chaplets are metal (with higher melting point than that of the cast metal) supports of various designs used to hold the core in place in the sand mold

There are various types of patterns used in sand casting. What is the difference between a split pattern and a match-plate pattern?

split- consist of two pieces, match- plate is two pieces of the split pattern are attached to opposite sides of a wood or metal plate

What are the most common metals used in die casting?

zinc, tin, lead, aluminum, brass and magnesium

What properties determine the quality of a sand mold for sand casting?

(1) strength - ability to maintain shape in the face of flowing metal. (2) permeability - ability of the mold to allow hot air and gases to escape from the cavity. (3) thermal stability - ability to resist cracking and buckling when in contact with the molten metal. (4) collapsibility - ability of the mold to give way during the shrinkage of the solidified casting.

Which of the following metals would typically be used in die casting (three best answers): (a) aluminum, (b) cast iron, (c) steel, (d) tin, (e) tungsten, and (f) zinc?

(a) aluminum (d) tin (f) zinc

In sand casting, the volumetric size of the pattern is (a) bigger than, (b) same size as, or (c) smaller than the cast part?

(a) bigger than the cast part

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

(b) CaSO4-H2O

Cupolas are furnaces used to melt which of the following metals (one best answer): (a) aluminum, (b) cast iron, (c) steel, or (d) zinc?

(b) cast iron

Which of the following qualifies as a precision-casting process (two correct answers): (a) ingot casting, (b) investment casting, (c) plastermold casting, (d) sand casting, and (e) shell molding?

(b) investment casting (c) plastermold casting

For which one of the following reasons is a green mold named: (a) green is the color of the mold, (b) moisture is contained in the mold, (c) mold is cured, or (d) mold is dry?

(b) moisture is contained in the mold

Silica sand has which one of the following compositions: (a) Al2O3, (b) SiO, (c) SiO2, or (d) SiSO4?

(c) SiO2

Which of the following casting processes are expendable mold operations (four correct answers): (a) centrifugal casting, (b) die casting, (c) investment casting, (d) low pressure casting, (e) sand casting, (f) shell molding, (g) slush casting, and (h) vacuum molding?

(c) investment casting (e) sand casting (f) shell molding (h) vacuum molding

A misrun is which one of the following defects in casting: (a) globules of metal becoming entrapped in the casting, (b) metal is not properly poured into the downsprue, (c) metal solidifies before filling the cavity, (d) microporosity, and (e) "pipe" formation?

(c) metal solidifies before filling the cavity

Which one of the following casting processes is the most widely used: (a) centrifugal casting, (b) die casting, (c) investment casting, (d) sand casting, or (e) shell casting?

(d) sand casting

Investment casting is also known by which one of the following names: (a) fast-payback molding, (b) full-mold process, (c) lost-foam process, (d) lost-pattern process, or (e) lost-wax process?

(e) lost-wax process

What are some of the general defects encountered in casting processes? Name and briefly describe three.

1. Misruns, in which the casting solidifies before filling the mold cavity 2. cold shuts, in which two portions of the metal flow together but there is lack of fusion at the joint 3. cold shots, where solid globules of cast metal become entrapped in the casing 4. shrinkage cavity, which is a depression on the casting surface or an internal void in the casting caused by solidification shrinkage 5. microporosity, which is a network of small voids throughout the casting caused by localized solidification shrinkage 6. hot tearing, which is a crack in the casting caused by a mold that does not yield to the metal during the early stages of solidification shrinkage

What is a cupola?

A cupola is a vertical cylindrical furnace equipped with a tapping spout near its base. Cupolas are used for melting cast iron.

Which of the following are advantages of die casting over sand casting (four best answers): (a) better surface finish, (b) closer tolerances, (c) higher melting temperature metals, (d) higher production rates, (e) larger parts can be cast, and (f) mold can be reused?

(a) better surface finish (b) closer tolerances (d) higher production rates (f) mold can be reused

Shell molding is best described by which one of the following: (a) casting operation in which the molten metal has been poured out after a thin shell has been solidified in the mold, (b) casting process in which the mold is a thin shell of sand bonded by a thermosetting resin, (c) sand-casting operation in which the pattern is a shell rather than a solid form, or (d) casting operation used to make artificial sea shells?

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

Which of the following casting processes are permanent mold operations (two correct answers): (a) centrifugal casting, (b) die casting, (c) expanded polystyrene process, (d) sand casting, (e) shell molding, (f) slush casting, and (g)vacuum molding.

(b) die casting (f) slush casting

Which one of the following casting metals is most important commercially: (a) aluminum and its alloys, (b) bronze, (c) cast iron, (d) cast steel, or (e) zinc alloys?

(c) cast iron

Given that Wm = weight of the molten metal displaced by a core and Wc = weight of the core, the buoyancy force is which one of the following: (a) downward force = Wm + Wc, (b) downward force = Wm - Wc, (c) upward force = Wm + Wc, or (d) upward force = Wm - Wc?

(d) upward force = Wm - Wc