Shape Casting

Question 1

How old does shape casting date back to?

Answer 1

5,000 BCE

Question 2

What are the 3 main benefits of Shape Casting?

Answer 2

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

Question 3

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

Answer 3

Negative

Question 4

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

Answer 4

bottom up, oxidation

Question 5

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

Answer 5

higher, 2-4%

Question 6

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

Answer 6

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

Question 7

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

Answer 7

eutectic composition

Question 8

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

Answer 8

material properties, lowered

Question 9

What is the major trade off in casting?

Answer 9

Castability for material properties

Question 10

Why do you want slow filling speeds in casting?

Answer 10

Laminar flow minimizes surface area and oxidation

Question 11

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

Answer 11

Reynolds Number

Question 12

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

Answer 12

500,000

Question 13

The downside of filling slowly is ____________ and ________________

Answer 13

slow production and cold running

Question 14

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

Answer 14

Cold Running

Question 15

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

Answer 15

gates and fill time,

Question 16

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

Answer 16

Slow, low, fast, high

Question 17

When casting cools it _________ in volume

Answer 17

reduces

Question 18

Volume reduction is highes in _____________ range

Answer 18

solidification

Question 19

What are the three phases that cooling occurs in?

Answer 19

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

Question 20

Tpouring to Tliquidus

Answer 20

specific heat - liquid phase,

Question 21

Liquid to solid phase transition (Tliquidus to Tsolidus)

Answer 21

Latent heat of solidification

Question 22

Tsolidus to RT

Answer 22

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

Question 23

What can be done about the
solidification shrinkage?

Answer 23

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

Question 24

What about the shrinkage that occurs after solidification?

Answer 24

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

Question 25

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

Answer 25

Chvorinov’s Rule

Question 26

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

Answer 26

underestimates

Question 27

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

Answer 27

4, underestimates, V/A, insulator

Question 28

What are the three main defects that affect casting?

Answer 28

porosity, internal stresses, distortion

Question 29

What are the two main causes of porosity?

Answer 29

Shrinkage porosity, Gas Bubbles

Question 30

_______________”: 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

Answer 30

Shrinkage Porosity, blocking

Question 31

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

Answer 31

Thinner

Question 32

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

Answer 32

temperature gradients

Question 33

________________ is the amount of thermal expansion or contraction

Answer 33

Thermal Strain

Question 34

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

Answer 34

Hookes law

Question 35

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

Answer 35

yield

Question 36

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

Answer 36

Simulations

Question 37

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

Answer 37

Alloy, Thickness Changes

Question 38

________________ 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

Answer 38

Casting Metallurgy

Question 39

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

Answer 39

powders, smaller, segregation

Question 40

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 “___________”

Answer 40

small, poisoning

Question 41

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

Answer 41

Sand Casting

Question 42

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

Answer 42

Parting Plane

Question 43

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

Answer 43

Sprue

Question 44

Sand cores allow manufacture of ________ products

Answer 44

hollow

Question 45

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

Answer 45

feeder

Question 46

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

Answer 46

Gravity Die Casting

Question 47

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

Answer 47

Low Pressure Die Casting

Question 48

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

Answer 48

High Pressure Die Casting

Question 49

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

Answer 49

Investment Casting

Question 50

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

Answer 50

crystalline, grain boundary

Question 51

Cast grains are typically _______ to _____ mm large

Answer 51

0.05, 5

Question 52

o Smaller grain size = _____________

Answer 52

Better Properties

Question 53

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

Answer 53

fast

Question 54

That are the 3 main reasons alloying elements are used?

Answer 54

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

Question 55

Alloying elements can introduce impurities that can be detrimental

Answer 55

Detrimental

Question 56

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

Answer 56

segregation

Question 57

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

Answer 57

Atomic Soup

Question 58

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

Answer 58

purer, enriched

Question 59

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

Answer 59

concentrated