Lecture 13 - Casting Processes

Question 1

Which casting process is also known as Lost Foam Casting?

Answer 1

Expendable Pattern Casting

Question 2

What type of pattern is used for expendable pattern casting? Briefly explain the process

Answer 2

• A polystyrene pattern which evaporates upon contact with the molten metal
• The molten metal is poured, pattern evaporates, and vents into permeable sand mold

Question 3

In expendable casting, what is expendable?

Answer 3

When molten metal is poured on the pattern, the pattern evaporates, therefore the pattern is expendable

Question 4

What are 3 advantages of expendable pattern casting?

Answer 4

• Simple process
  
  • Does not require parting lines, cores, risers, and minimal finishing
• Patterns are inexpensive
• Good for long production runs

Question 5

How are patterns created in expendable pattern casting? What about complex patterns?

Answer 5

• Metal dies
• Complex patterns can be obtained by bonding multiple parts together

Question 6

In expendable pattern casting, what is the pattern coated with?

Answer 6

The Pattern is coated in a refractory metal slury, dried, and placed in a container of compacted sand

Question 7

Investment Casting is also known as…?

Answer 7

Lost wax casting

Question 8

With regards to the pattern, what is the difference between investment casting and expendable casting? (Not talking about the material)

Answer 8

• The wax pattern is removed prior to casting
• Wax pattern is melted out as the mold cures allowing for a stronger mold

Question 9

Comparing investment casting to expendable casting, which one costs more? Which one is more automatable?

Answer 9

Investment casting costs more and and expendable casting is more automatable

Question 10

Both investment casting and expendable casting can be classified as “___“-Mold, “___“-Pattern Casting

Answer 10

Expendable, Expendable

Question 11

Advantages of investment casting

Answer 11

• Large range of part sizes may be cast
• Little to no finishing is necessary
• Creates stronger molds than lost foam/expendable casting

Question 12

Disadvantages of investment casting

Answer 12

• High labour
• High material cost

Question 13

Slush Casting utilizes what property? What is the result of applying this concept?

Answer 13

• According to Chvorinovs rule, a piece begins to solidfy at the edges and becomes thicker with time.
• Using this concept, the remaining slush that still has yet to cool can be poured out which allows for thin walled, hollow castings to be made

Question 14

What is slush casting suitable for? What kind of metals?

Answer 14

• Low production runs of non-structural components in materials
• Zinc, tin, and lead alloys (ie low melting point alloys)

Question 15

In die casting, molten metal is “____” into a “__ ____”. What is the pressure range during this process?

Answer 15

Molten metal is “forced” into a “die cavity” at pressures of 0.7-700MPa

Question 16

What are the two types of chambers used in Die Casting?

Answer 16

Hot and Cold chambers

Question 17

Briefly describe the process of a hot chamber in Die casting?

Answer 17

Metal is kept in a furnace pot, and forced into the mold by a plunger and held under pressure until solidifed

Question 18

In die casting, hot chambers are suitable for…? And has a “___” production rate

Answer 18

• Suitable for low melting alloys
• High production rate

Question 19

What is a Cold Chamber with respect to Die Casting?

Answer 19

Metal is put into a shot chamber that is NOT heated

Question 20

What type of metals would you use for cold chamber, in die casting? Name examples

Answer 20

Useful for high temp alloys such as Cu, Al, and ferrous metals

Question 21

What type of forces are used in centrifugal casting?

Answer 21

Utilizes inertial force caused by rotation to force metal into a mold cavity

Question 22

What role does density play in centrifugal casting?

Answer 22

Heavier particles will go to the outer radius of the mold.

Question 23

In centrifugal casting, what causes impurites to be collected? What are some impurities likely to be present and how are they removed?

Answer 23

• Due to density differences, impurities collect at a certain radius
• Can be useful for collecting impurities like dross (whic is oxides solidfied) and fluxes which is removed by finish machining

Question 24

What two processes does Squeeze Casting incorporate?

Answer 24

Casting and Forging

Question 25

In Squeeze Casting, molten metal solidies in a die cavity at “___” pressures, resulting in…?

Answer 25

• “High”
• Fine Microstructure
• Good Mechanical Properties
• Little to no porosity

Question 26

Squeeze casting uses (higher/lower) pressures than forging and (higher/lower) pressures than die casting

Choose Higher or Lower

Answer 26

• Lower
• Higher

Question 27

Name applications of squeeze casting

Answer 27

Car wheels, brake drums, valve bodies

Question 28

What is an advantage of Squeeze Casting in terms of design?

Answer 28

Near net shape materials can be produced with complex shapes and fine detail

Question 29

When casting gas turbine blades, what kind of crystal structure is present and where within the crystal structure does the grain fail?

Answer 29

• Polycrystalline stucture
• Failure occurs along the grain boundaries

Question 30

What type of solidifcation does gas turbine casting use?

Answer 30

Directional solidification

Question 31

Briefly describe the process of Directional Solidication for the casting of gas turbines blades

Answer 31

Direction solidication involves slow cooling from a chill plate, while the part is kept hot by radiant heat

Question 32

In casting gas turbine blades, directional solidification results in what type of grains?

Answer 32

• Columnar Grains
  
  • With high strength in the longitudinal direction

Question 33

In gas turbine blades, how can parts be cast as single crystals?

Answer 33

By allowing only one crystal to pass and solidfy