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MET166 > expendable mold > Flashcards

expendable mold Flashcards

1
Q

What are the 6 expendable mold processes?

A
  1. Shell molding
  2. Vacuum molding
  3. Expanded polystyrene- mold casting
  4. Investment casting
  5. Plaster mold casting
  6. Ceramic mold casting
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2
Q

Is a casting process in which the mold is a thin shell (typically 9mm or 3/8 in) made of sand held together by a thermosetting binder

A

Shell molding

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3
Q

What is shell molding?

A

Is a casting process in which the mold is a thin shell (typically 9mm or 3/8 in) made of sand held together by a thermosetting binder

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4
Q

It was developed in Germany during the early 1940s.

A

Shell molding

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5
Q

What are the advantages of shell molding?

A
  • shell mold cavity is smoother than a conventional green sand mold.
  • better surface finish (finishes of 2.5 micrometers)
  • good dimension accuracy (tolerance of +-0.25 mm)
  • collapsibility is sufficient
  • thin wall thickness and complex castings
  • less manpower and molding skill requirement
  • mass production
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6
Q

What are the disadvantages of shell molding?

A
  • more expensive metal pattern than green sand mold
  • high production costs and casting prices
  • size and weight limitation (less than 20 lb)
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7
Q

Examples of the application of shell molding.

A

gears, valve bodies, brushings, and camshafts

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8
Q

Vacuum molding is also called as ____________.

A

V- process

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9
Q

It was developed in Japan around 1970.

A

Vacuum molding

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10
Q

It uses a sand mold held together by a vacuum pressure rather than by a chemical binder.

A

Vacuum molding

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11
Q

What is vacuum molding?

A

It uses a sand mold held together by a vacuum pressure rather than by a chemical binder.

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12
Q

What are the advantages of vacuum molding?

A
  • sand is readily recovered
  • does not need extensive mechanical reconditioning
  • moisture-related defects are absent
  • surface quality
  • dimensional accuracy
  • unlimited pattern life
  • design quality
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13
Q

What are the disadvantages of vacuum molding?

A
  • relatively slow
  • not readily adaptable to mechanization
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14
Q

It uses a mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold.

A

Expanded polystyrene mold-casting

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15
Q

What is expanded polystyrene mold casting?

A

It uses a mold of sand packed around a polystyrene foam pattern that vaporizes when the molten metal is poured into the mold.

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16
Q

The process and variations of it are known by other names, including _____________.

A

*lost- foam process
*lost- pattern process
*evaporative- foam process
*full- mold process

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17
Q

In EPM, the foam pattern includes ________.

A

sprue, risers, and gating systems, also internal cores

18
Q

In EPM, the form patter excludes _______.

A

draft, parting lines

19
Q

In EPM, the pattern is usually coated with _______. Why?

A

refractory compound: to provide a smoother surface on the pattern and to improve its high-temperature resistance.

20
Q

What are the advantages of EPM casting?

A
  • the pattern needs not to be removed from the mold
  • molding sand can be reused
  • complex shapes without the use of cores
  • no parting line
  • good surface finish, high dimensional accuracy
  • low-cost production
  • process is relatively simple and straightforward
21
Q

What are the disadvantages of EPM casting?

A
  • a new pattern is needed for every casting
  • pattern density
  • low strength, and susceptible to damage
  • econ justification is highly dependent on the cost of producing products
22
Q

This uses a pattern made of wax which is coated with a refractory material to make the mold. After which, the wax is melted away prior to pouring the molten metal.

A

Investment casting

23
Q

What is investment casting?

A

This uses a pattern made of wax which is coated with a refractory material to make the mold. After which, the wax is melted away prior to pouring the molten metal.

24
Q

In investment casting, the word ‘investment’ comes from the word ‘invest’ which means ______________.

A

to cover completely; this refers to the coating of the refractory material around the wax pattern.

25
Q

What are the advantages of investment casting?

A
  • precision casting
  • casts with high accuracy and intricate detail
  • a very smooth surface finish is obtained with no parting line
  • dimensional accuracy is good
  • a wide variety of metals and alloys can be cast
  • low material waste
  • it may be used to replace die- casting where short runs are involved
26
Q

What are the disadvantages of investment casting?

A
  • size limitation
  • the process is expensive
  • holes cannot be small
  • high labor cost
  • require a very long production cycle (many processing steps required)
  • infeasible for high-volume manufacturing
  • a separate pattern mus be made for every casting
27
Q

The investment casting process dates back to _______.

A

ancient Egypt

28
Q

Investment casting is also known as _____________.

A

lost- wax process; because the wax pattern is lost from the mold prior to casting

29
Q

In investment casting, the pattern production is usually accomplished by a molding operation; pouring or injecting the hot wax into a ____________ that has been designed with proper allowances for shirnkage of both wax and subsequent metal casting.

A

master die

30
Q

In investment casting, especially in high- production operations, several patterns are attached to a sprue, also made of wax, to form a ____________, this is the geometry that will be cast out of metal.

A

pattern tree

31
Q

It is similar to sand casting except that the mold is made of plaster of Paris (gypsum-CaSo4-2H2O) instead of sand.

A

Plaster mold casting

32
Q

Additives such as ________ and _______ are mixed with the plaster to control contraction and setting time, reduce cracking, and increase strength.

A

talc; silica

33
Q

What is plaster mold casting?

A

It is similar to sand casting except that the mold is made of plaster of Paris (gypsum-CaSo4-2H2O) instead of sand.

34
Q

What are the advantages of plaster mold casting?

A
  • good surface finish and a high degree of dimensional accuracy
  • can form large parts with less expense than investment casting
  • additives also add strength and prevent cracks
  • allows the fabrication of more complicated parts
  • make thin cross-sections
35
Q

What are the disadvantages of plaster mold casting?

A
  • new mold is needed every time for plaster mold casting
  • more expensive than most sand-casting operations
  • can’t withstand the same high temperatures as sand molds
    limited to the casting of lower-melting point alloys (Al, Mg, Cu base alloys)
  • maximum working temperature of plaster is 1200 deg C
  • only for non-ferrous alloy castings
  • poor productivity
  • mold strength is lost once plaster dehydrates
  • casting defects due to moisture content
  • poor mold permeability
36
Q

It is similar to plaster mold casting, except that the mold is made of refractory ceramic materials that can withstand higher temperatures than plaster.

A

Ceramic mold casting

37
Q

What is ceramic mold casting?

A

It is similar to plaster mold casting, except that the mold is made of refractory ceramic materials that can withstand higher temperatures than plaster.

38
Q

What are the advantages of ceramic mold casting?

A
  • good surface finish
  • good dimensional accuracy
  • mass production
  • industry and home foundry
  • withstand extremely elevated temperatures
  • excellent permeability
  • relatively intricate parts
39
Q

What are the disadvantages of ceramic mold casting?

A
  • relatively expensive
  • long preparation of the mold
40
Q

The ceramic mold casting can be used in ______.

A

steels, cast irons, and other high-temperature alloys

MET166 (9 decks)

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