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Bang the 322 Midterm Flachcards > Casting > Flashcards

Casting Flashcards

ANY SHAPE!

1
Q

What shape can be casted?

A

ANY SHAPE!

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2
Q

What are the capabilities/advantages of casting?

A
  1. complexity (any shape)
  2. net shape (single step process)
  3. size
  4. material
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3
Q

What are the 2 types of casts?

A
  1. expandable mold (can’t be reused)
  2. permanent mold (can be reused)
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4
Q

Disadvantages of casting

A
  • mechanical properties
  • poor dimensional accuracy and finish
  • shrinkage, porosity, cracks
  • expensive permanent mold
  • microstructures hard to control
  • not uniform
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5
Q

What are the6 basic requirements for casting process?

A
  1. mold cavity
  2. melting process
  3. pouring technique
  4. solidification process
    cleaning, finishing, inspection operations
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6
Q

What are the two halves of a mold?

A
  1. Cope = upper half
  2. Drag = lower half
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7
Q

What does a riser do?

A

holds extra material and solidifies last, minimizes shrinkage and creates pressure

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8
Q

What do the down sprue and pouring cup do?

A

minimizes turbulence and controls flow rate

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9
Q

Purpose of a draft angle

A

allows material to be removes from the casting

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10
Q

Pouring temperature has to be… (for pure metals)

A

much higher than m.p., so it doesn’t solidify fast

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11
Q

Local solidification time (for pure metals)

A

freezing begins to freezing finishes (all at melting point)

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12
Q

Total solidification time (for pure metals)

A

time from pouring to freezing temperature

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13
Q

Relationship between melting points and freeze speed

A

high m.p. freezes first, low m.p. freezes last

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14
Q

Do alloys and metals freeze the same?

A

No. Alloys have a freezing range, not point

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15
Q

What happens in alloy segregation?

A
  • columnar zone, dendrites, has metal with high m.p.
  • equiaxed zone, center then has very no high m.p. metals
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15
Q

What is used to minimize alloy segregation?

A

cooling rate and nucleating agents, mechanical means, EM stirring

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16
Q

Better to have a high or slow cooling rate?

A

High is better since it has a shorter solidification time

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17
Q

What does a slow cooling rate cause?

A

coarse dendritic structures (large spacing between dendrite arms)

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18
Q

What does a high cooling rate cause?

A
  1. small dendrites
  2. large equiaxed zone
  3. small grain size (strength and ductility increase, micro-porosity decreases)
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19
Q

Chorinov’s Rule (solidification time)

A

TST = Cm(V/A)^n

V - volume
A - surface area
n=2
Cm - mold constant

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20
Q

Fluidity (fill mold before freezing) is affected by the following 4:

A
  1. viscosity
  2. surface tension
  3. inclusion
  4. freezing range
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21
Q

How to ensure riser solidifies last

A

(V/A)Riser > (V/A)Casting

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22
Q

At what stage does shrinkage happen?

A

All stages! pouring, freezing, and cooling

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23
Q

What is shrinkage allowance?

A

making the pattern a lil bigger to make mold bigger

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24
What is solidification toward in directional solidification?
the riser
25
What can external chills do?
induce chilling effect, causing directional solidification
26
Velocity of liquid eqn:
v = sqrt(2gh)
27
What is volumetric flow rate (Q)?
Q = vA v - velocity A - area
28
What is time required to fill a mold?
T = V/Q V - mold cavity volume Q - volumetric flow rate
29
What is aspiration in casting?
as metal goes down sprue and velocity increases, unwanted air goes into mold
30
to determine the minimal cross sectional area of the taper at any point, what eqn is used?
A1/A2 = sqrt(h2/h1) assuming pressure above and below are equal
31
What is gates in casting?
the passages where the molten material goes into a mold
32
How should a gate be designed?
- multiple gates for large parts - should feed into thick sections of casting - fillets for where gate and casting meet (less turbulence) - gate closet to sprue should be far enough to remove - minimum gate length should be 3 to 5 times the gate diameter, depending on metal being casted
33
What are different types of expandable molds?
1. sand molds 2. shell molds 3. vacuum molds 4. plaster molds 5. investment molds
34
What are the different reusable molds
1. permanent molds 2. die casting 3. centrifugal casting
35
pros and cons of sand casting:
pros - many metals, sizes, shapes, cheap - high temps - high volume cons - poor finish and tolerance - automation isn't easy
36
What are casting, sand properties
- cohesiveness - strength - permeability - thermal stability - collapsibility - reusability
37
What is typical mix of sand binders?
90% sand (SiO2), 7% clay, 3% water
38
3 types of sand molds:
- green sand (sand, clay, water) - dry sand (organic binders not clay) - skin dried
39
What is the pattern?
full sized model of part
40
The 3 pattern materials
1. wood 2. metal 3. plastic
41
The 4 pattern types (worst to best)
1. solid pattern 2. split pattern 3. match plate pattern 4. cope and drag pattern
42
What holds a core in place?
chaplets and they have a higher melting temp
43
Is sand casting net shape?
no , it's near net shape as it needs trimming and removal of core
44
The 2 different types of sand casting
1. shell molding (no porosity, better finish, too expensive) 2. vacuum mold (takes time, better finish, no porosity)
45
Expanded Polystyrene Process
when you use the polystyrene beads in a die, take out and coat it, then pour molten metal. - very good surface finish, cheap, high volume manufacturing, porosity problems minimized - cost of die is very expensive
46
What is investment casting?
when a pattern of wax is coated with a refractory material to make mold, then wax is melted away before pouring molten metal
47
What's the difference between Expanded Polystyrene Process and investment casting?
polystyrene uses beads, investment casting uses wax
48
What type of finish does investment casting give?
- no porosity issues - VERY GOOD SURFACE FINISH - used for medical tools - very expensive - too many steps
49
What's the difference between plaster mold vs sand mold
plaster has better finish and accuracy but worst porosity and can't withstand high temps
50
Pros of ceramic finish:
- good surface finish and porosity - can with stand high temp
51
What do you base your choice on when it comes to sand, platter, or ceramic casting?
this is based on the melting point of the material
52
What material do permanent molds use?
instead of sand they use a metal mold
53
What happens when you use metal?
gives you the wall situation with the chill zone
54
Processes of permanent mold casting
1. basic permanent mold process 2. die casting 3. centrifugal casting
55
Basic permanent mold process
use metal for 2 sections, mold must withstand the temp
56
Die casting
applying high pressure, throughout processes till it solidifies
57
Centrifugal casting
by rotating mold at high, uses centrifugal force to distribute molten material
58
The 3 groups of inertial forces caused by rotation
1. true centrifugal casting 2. semi-centrifugal casting 3. centrifuge casting
59
What are slush castings used for?
used for hollow structures because it doesn't allow for everything to solidify
60
The 4 extra general defects:
1. misrun 2. cold shut 3. cold shot 4. shrinkage cavity
61
Cold shut
2 portions of metal flow together but lack of fusion due to premature freezing
62
Cold shot
metal splatters during pouring and becomes trapped in casting
63
Shrinkage cavity
depression in surface caused by solidification shrinkage that restricts the amount of molten metal available in last region to freeze
64
Misrun
casting that solidifies before completely filling mold cavity
65
Foundry inspection methods
1. any defects 2. does it meet specification (measurements) 3. does it have the metallurgical/chemical/physical properties

Bang the 322 Midterm Flachcards (2 decks)

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