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MCHE 3920 Final > Shape Casting > Flashcards

Shape Casting Flashcards

1
Q

How old does shape casting date back to?

A

5,000 BCE

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2
Q

What are the 3 main benefits of Shape Casting?

A
  1. Large form freedom
  2. Retain properties at elevated temp
  3. Distinct character and Texture
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3
Q

In casting, Liquid metal is poured into a mold that defines the
______________of the product

A

Negative

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4
Q

When casting, it is best to fill the mold “_________” to prevent
splashing (and thus _________ and loss of material
properties) and helps prevents gas entrapment

A

bottom up, oxidation

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5
Q

Castings generally have _________ alloy content
o e.g.: Steel (Fe< 2% carbon) is not typically cast,
but cast iron (Fe with ______ carbon is)

A

higher, 2-4%

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6
Q

What are the two reasons for higher alloy content in castings?

A

Lower viscosity (Better mold filling), Lower melting temperature (Lower energy, Faster throughput)

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7
Q

Want casting metals to be near ______________
* Homogeneous composition and lowest possible
melting temp and typically lower viscosity

A

eutectic composition

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8
Q

Higher alloy content comes at expense of
______________ such as Toughness, ductility and fatigue strength being reduced by presence of alloy
o In cast iron, stiffness is also __________relative to low carbon steel

A

material properties, lowered

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9
Q

What is the major trade off in casting?

A

Castability for material properties

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10
Q

Why do you want slow filling speeds in casting?

A

Laminar flow minimizes surface area and oxidation

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11
Q

What is the transition from laminar to turbulent flow predicted with?

A

Reynolds Number

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12
Q

For flow over a flat plate, the transition is typically Re=_______________

A

500,000

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13
Q

The downside of filling slowly is ____________ and ________________

A

slow production and cold running

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14
Q

_____________ is when parts of the mold solidify before all of the mold is filled

A

Cold Running

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15
Q

You can prevent cold running by increasing ______________ and ___________________ but those require more Finishing after and increased cost and weight.

A

gates and fill time,

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16
Q

Casting is usually ________ at ________ pressures and _____ at ________ pressures

A

Slow, low, fast, high

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17
Q

When casting cools it _________ in volume

A

reduces

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18
Q

Volume reduction is highes in _____________ range

A

solidification

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19
Q

What are the three phases that cooling occurs in?

A

Tpouring to Tliquidus, Liquid to solid phase transition (Tliquidus to Tsolidus), Tsolidus to RT

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20
Q

Tpouring to Tliquidus

A

specific heat - liquid phase,

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21
Q

Liquid to solid phase transition (Tliquidus to Tsolidus)

A

Latent heat of solidification

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22
Q

Tsolidus to RT

A

Specific Heat, solid phase (J/(kg-k))

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23
Q

What can be done about the
solidification shrinkage?

A

Add extra material during filling (known as “feeding”)

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24
Q

What about the shrinkage that occurs after solidification?

A

Make the mold bigger (typically 1%-2%)

25
Q

_____________________ determines how long it takes before part is cool enough
and strong enough to be handled?

A

Chvorinov’s Rule

26
Q

Chvorinov’s rule works well for large solid castings, but it
_________________time for hollow and thin-walled parts

A

underestimates

27
Q

For thin walled parts (< _____mm thick), chvorinov’s rule very much
_______________ solidification and cooling time.
* A better model is proportional to_____
* Because the mold expands while the casting contracts
creating an air gap that acts like an _________ limiting

A

4, underestimates, V/A, insulator

28
Q

What are the three main defects that affect casting?

A

porosity, internal stresses, distortion

29
Q

What are the two main causes of porosity?

A

Shrinkage porosity, Gas Bubbles

30
Q

_______________”: Not enough extra material
is fed into the casting to compensate for
solidification shrinkage
* Can happen when a thin section of a mold or a
poorly designed runner solidifies thus ________ flow into the thicker section
* Can be avoided with good mold and filling
design

A

Shrinkage Porosity, blocking

31
Q

Think about cooling time being related to V/A
* Which cools more quickly, thinner sections or
thicker sections?

A

Thinner

32
Q

Different sections with different thicknesses will cool at different rates which leads to _________________ within the casting

A

temperature gradients

33
Q

________________ is the amount of thermal expansion or
contraction

A

Thermal Strain

34
Q

Local differences in temperature will therefore cause
differences in contraction, these differences cause
stresses by __________ Law

A

Hookes law

35
Q

If the casting is free to deform and the stresses exceed
the________ stress, permanent deformation can occur

A

yield

36
Q

Predicting internal stresses and/or deformation often
requires ________________because of complex
geometries involved

A

Simulations

37
Q

The issues of porosity, internal stress and distortion can
typically be mitigated through careful selection of _______
and design of part to avoid large ___________________

A

Alloy, Thickness Changes

38
Q

________________ is the process of choosing the best alloy for the job
* Large field with a lot of “tricks” and rules of thumb
developed over the years

A

Casting Metallurgy

39
Q

Inoculants are high melting point __________ added before pouring
o As liquid cools, solids form around the inoculant,
promoting ________ grains and less __________

A

powders, smaller, segregation

40
Q

Sometimes ________ additions of the right element
can dramatically improve the tensile strength of a cast
metal (e.g., trace amounts of sodium in Al castings)
o Called “___________”

A

small, poisoning

41
Q

What casting method is this?
Very cheap
o Can be made to a wide range of sizes
o Rather fragile and only support low filling
speeds and pressures
o Long solidification times = larger grains
o Rough surface properties
o Poor tolerances

A

Sand Casting

42
Q

Plane where drag and cope meet is
called the “__________”

A

Parting Plane

43
Q

What is the down ward channel is a casting mold called?

A

Sprue

44
Q

Sand cores allow manufacture of
________ products

A

hollow

45
Q

Riser (aka “_______”) shows when filling is complete and helps allow
for shrinkage

A

feeder

46
Q

What method is of casting is this?
Shorter cycle times = Finer microstructure
o Smoother products and good control over tolerances
o Filling speeds are low
o Product size more limited than sand casting
o Aluminum and magnesium are commonly cast using this method

A

Gravity Die Casting

47
Q

What method is of casting is this?
Also uses reusable steel dies
o Pressures from 2 to 5 bar
o Good reproduction of die details
o Dies often placed on top of furnace and fed through riser tube using gas pressure
o Aluminum & magnesium are also commonly cast using this method

A

Low Pressure Die Casting

48
Q

Uses very expensive steel dies
o Pressures up to 2000 bar
o Cannot use Sand cores
o But can use sliding elements to
make undercuts
o Injection speed are high
o Fast throughput
o Low quality
o Thinner products
o Limited to Zink, aluminum,
and magnesium

A

High Pressure Die Casting

49
Q

Relatively rare method
o Pattern made of wax and attached to the sprue
o Dipped into a ceramic slurry that cures while the
wax melts away
o The hollow ceramic shell is used as the mold
o After casting, shell is destroyed to remove part
o Very time consuming process
o Good for very complex geometries

A

Investment Casting

50
Q

Metals have a __________ grain structure
o Grains grow within solid and along mold wall and where
they impinge on each other is the _____________

A

crystalline, grain boundary

51
Q

Cast grains are typically _______ to _____ mm large

A

0.05, 5

52
Q

o Smaller grain size = _____________

A

Better Properties

53
Q

Grain size is largely dictated by cooling rate
o ________ cooling leads to smaller grains

A

fast

54
Q

That are the 3 main reasons alloying elements are used?

A
  1. Improve processability (e.g., low viscosity or
    melt temp)
  2. Improve material properties (e.g., strength)
  3. Minimize effects of impurities or improve
    microstructure
55
Q

Alloying elements can introduce impurities that can be
detrimental

A

Detrimental

56
Q

___________________ is the name given to the non-uniform
distribution of dissolved elements during solidification

A

segregation

57
Q

In the liquid state, alloy elements are dissolved in an
“____________”

A

Atomic Soup

58
Q

During cooling, the first solids to form will be _________than average, so the remainder is
relatively _________ which will lead to impurities

A

purer, enriched

59
Q

The last part to solidify will be the grain boundaries
so the impurities tend to be ___________near the
grain boundaries

A

concentrated

MCHE 3920 Final (10 decks)

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