Me 350 Exam 2

Front 1

Limitations of Casting

Back 1

1) Non-ideal mechanical properties
2) Poor dimensinoal accuracy and surface finish
3) Safety Hazards (molten Metal)

Front 2

Two categories of Casting Processes

Back 2

1) Expendable mold
2) Permanent Mold

Front 3

Top half of mold

Back 3

Cope

Front 4

Bottom Half of mold

Back 4

Drag

Front 5

Box containing mold

Back 5

Flask

Front 6

Where the two halves of the mold separate

Back 6

Parting line

Front 7

Function of Riser

Back 7

It acts as a source of liquid metal to compensates for shrinkage during solidification

Front 8

Does the riser freeze before or after the main casting?

Back 8

After

Front 9

Heating the metal

Back 9

*Heat to get metal to Tm
*heat of fusion to convert from solid to liquid
* heat to raise molten metal to desired temp

Front 10

Equation for velocity of metal at base of sprue

Back 10

v = sqrt(2*(981.5 cm/s^2)*h)

Where h = height of sprue

Front 11

Equation for Continuity of flow

Back 11

v1A1 = v2A2

Front 12

Equation for Mold fill time

Back 12

T_mf = V/Q

Front 13

Why is the sprue tapered?

Back 13

To prevent air from becoming entrapped in the metal

Front 14

What is the velocity assumed to be in the pouring cup?

Back 14

Zero!

Front 15

What is the difference between the cooling of an alloy and a pure metal?

Back 15

Pure metal: constant temp during solidification
Alloy: decreasing temp during solidification

Front 16

Equation for casting solidification time (Chvorinov's rule)

Back 16

T = C (V/A)^n

where n=2

Front 17

The mold constant Cm depends on:

Back 17

1) Mold Material
2) Thermal properties of metal
3) Pouring temp relative to melting point

Front 18

Solidification time and Riser design

Back 18

> Riser Must have a larger Tts
> Must have larger V/A ratio
> Minimizes effect of Shrinkage

Front 19

Equation for Solidification shrinkage

Back 19

Vf = Vo(1-alpha)(1-beta)

Front 20

Equation for linear dimension change from solidification shrinkage

Back 20

Lf = Lo((1-alpha)(1-beta))^(1/3)

Front 21

Directional Solidification

Back 21

It is desirable that regions most distant from the liquid metal supply freeze first

Front 22

Purpose of Chills

Back 22

-internal or external heat sinks that cause rapid freezing in certain regions of the casting.

Front 23

What is a pattern?

Back 23

A model of the part to be casted, slightly enlarged to account for shrinkage and machining allowances

Front 24

What is a core?

Back 24

A full scale model of interior surfaces of part.
* May require supports called chaplets to hold it in place

Front 25

Equation for core buoyancy

Back 25

Fb = Wm - Wc

Where Wm = weight of liquid metal displaced
and
Wc = weight of core

Front 26

Desirable mold Properties

Back 26

1) Strength-to resist erosion
2) Permeability - to allow hot air and gasses to escape
3) Thermal Stability - to resist cracking when contacting metal
4) Collapsiblity - allow casting to shrink without cracking it
5) Reusability - reusing material to make other molds

Front 27

Foundry Sands

Back 27

Silica sand
1) good refractory properties
2) Small grain size for better surface finish
3) large grain size is more permeable

Front 28

Advantages and Disadvantages of irregular grain size

Back 28

Advantage: interregular grain shapes strengthen molds
Disadvantage: interlocking tends to reduce permeability

Front 29

What is green sand?

Back 29

Sand with moisture in it

Front 30

What is a dry sand mold

Back 30

It uses organic binders instead of clay--Must Be Baked!!!!

Front 31

Skin dried mold

Back 31

drying mold cavity surface of a green sand mold

Front 32

Pros and Cons of Shell molding

Back 32

Pros:
1) smoother cavity surface permits easier flow of molten metal and better surface finish
2) good dimensional accuracy-machining often not required
3) less cracks in casting
CONS:
1) Takes more time
2) Because of resin, more expensive
3) shell not reusable

Front 33

Pros and Cons of expanded Polystyrene process

Back 33

PROS:
1) Pattern need not be removed from the mold
2) Faster: two halves are not required
CONS
1) a new pattern is needed for every casting
2) Cost is highly dependent on cost of producing patterns

Front 34

Pros and Const of investment Casting

Back 34

PROS:
1) very complex parts can be cast
2) Close dimensional control and good surface finish
3) wax can be recovered for reuse
4) Additional machining not normally required--NET SHAPE PROCESS
CONS
1) many processing steps required
2) relatively expensive process

Front 35

Pros and Cons of Permanent mold casting

Back 35

PROS
1) Good dimensional control and surface finish
2) more rapid solidification caused by the cold metal causes finer grain structure and stronger casting
CONS
1) Limited to metals with lower melting points
2) need to open mold requires simpler geometries
3) High cost of mold

Front 36

Possible casting defects and flaws

Back 36

1) misruns & cold shuts
2) cold shot
3) shrinkage cavity
4) sand blow and pin holes
5) Penetration

Front 37

Misrun and Cold shut

Back 37

Misrun - metal solidifies before completely filling
Cold Shut - metal has flowed together but failed to fuse
SOLUTION:
increase sand permittivity, increase pour temp, increase height of downsprue

Front 38

Cold Shot

Back 38

Metal splatters during pouring and oxides become entrapped in casting
* on the interior of the casting
SOLUTION: Increase pouring cup diameter or slow down pour

Front 39

Shrinkage Cavity

Back 39

Depression in surface or internal void caused by solidification shrinkage that restricts amount of molten metal available in last region to freeze
SOLUTION:
Increase riser volume/surface area ratio

Front 40

Sand Blow and Pin Holes

Back 40

Balloon shaped gas cavity or many small gas cavities just below the surface.
SOLUTION:
Decrease pour temp or increase sand permittivity

Front 41

Penetration

Back 41

Molten liquid penetrates into sand causing surface to consist of mixture of sand grains and metal
SOLUTION
Decrease pour temp or decrease sand permittivity

Front 42

Casting product design considerations

Back 42

1) geometric simplicity that allows for shrinkage and reduces the need for cores
2) Reduce sharp angles to reduce stress concentrations that may cause cracking
3) Increase draft angles
4) Dimensional tolerances and surface finish
5) machining allowance

Front 43

Die Casting

Back 43

Permanent mold casting process in which molten metal is injected into mold cavity under high pressure

Front 44

Centrifugal Casting

Back 44

a family of casting processes in which the mold is rotated at high speed so centrifugal force distributes molten metal to outer regions of the die cavity

Front 45

Definition: Steel

Back 45

Iron-Carbon alloy containing from 0.02% to 2.1% carbon

Front 46

Definition: Cast Iron

Back 46

Iron-Carbon alloy containing from 2.1% to 4.3% carbon

Front 47

Stainless Steel properties and composition

Back 47

Properties:
Corrosion Resistant
Composition:
>greater than 15% chromium
>nickel

Front 48

Bronze composition

Back 48

90% Cu, 10% Sn

Front 49

Brass composition

Back 49

65% Cu, 35% Zn

Front 50

Beryllium-copper

Back 50

2% Be, strongest copper alloy

Front 51

What does it mean if something is galvanized?

Back 51

Steel coated with Zinc to increase corrosion resistance

Front 52

Refractory Metals

Back 52

-Maintain high Strength and hardness at elevated temps
> molybdenum
> Tungsten
> Tantalum
> Titanium?

Front 53

Definition: Superalloys

Back 53

> High performance metals
> composed of substantial amounts of 3 or more metals

Front 54

How to Enhance Mechanical Properties

Back 54

> Alloying -adding additional elements to increase the strength of metals
> Cold working
> Heat Treatment

Front 55

What special material property (involving viscosity) do plastics have?

Back 55

They are shear thinning

Front 56

What is the property that produces Die Swell in plastics

Back 56

Viscoelesticity

Front 57

Die Swell Equation

Back 57

Rs = Dx / Dd

Where
Dd = die diameter
Dx = extrudate diameter

Front 58

Name the sections of an extruder from hopper to die

Back 58

1) Feed Section
2) compression section
3) Metering Section
4) breaker plate?
5) die

Front 59

Functions of the Screen Pack in extruding

Back 59

Functions
1) Filter (remove contaminants and any hard lumps)
2) Building pressure in the metering section
3) Straighten flow " remove memory of circular flow from screw"

Front 60

How does die swell effect the extrusion of pipes?

Back 60

Both the inside diameter and outside diameter swell according to the die swell equation.

Front 61

How are hollow parts extruded?

Back 61

Through the use of a spider mandrel. The gaps created are closed by the die swell of the plastic

Front 62

How does sheet and film production work with plastics?

Back 62

Feedstock is passed through a series of rolls to reduce thickness to desired gage

Front 63

Cycle times for injection molding

Back 63

1-30 sec

Front 64

What types of plastics are used for injection molding

Back 64

Thermoplastics, thermosets, elastomers

Front 65

Advantages of three plate over two plate molds

Back 65

> as mold opens, runner and parts disconnect and drop into two separate containers
> Allows automatic operation of molding machine
> allows material to be injected at the mold base or middle rather than the side

Front 66

Modifications for injection molding of thermosets

Back 66

> Lower injector temps
> Shorter barrel length
> most time consuming step is curing

Front 67

Compression Molding

Back 67

>widely used process for thermosets
>amount of charge precisely controlled

Front 68

Mold restrictions for compression molding

Back 68

> limited to simpler part geometries
> mold must be heated

Front 69

Other types of plastic molding

Back 69

>Compression Molding
>Transfer molding
> Blow Molding
> Extrusion blow molding
>injection blow molding
> vacuum thermoforming
> polymer casting

Front 70

Design Guidelines: Strength and Stiffness of plastics

Back 70

> not as strong as metals
> creep resistance limited
> competitive strength to weight ratios

Front 71

Design Guidelines: Impact resistance, Service temps, thermal expansion of plastics

Back 71

> plastics generally have good impact resistance
> limited service temps
> much greater thermal expansion than for metals

Front 72

General plastic design guidelines

Back 72

>subject to sunlight degradation
> degrade in oxygen sometimes
> soluble in common solvents
> resistant to many corrosion mechanisms

Front 73

Advantages of composites

Back 73

>Strength to Weight ratio are several times greater than for steel or aluminum
> Better Fatigue Properties
> Toughness is greater
> different combinations of properties achievable

Front 74

Disadvantages of composites

Back 74

> properties are anistropic
> weakened by chemicals or solvents
> expensive
>manufacturing is slow

Front 75

Phases of a composite

Back 75

1) Primary or matrix phase
2) secondary or reinforcing phase

Front 76

Types of composites

Back 76

> Metal Matrix composites (MMC's)
> Ceramic Matrix Composites (CMC's)
> Polymer Matrix Composites (PMC's)

Front 77

Fiber orientation types in composites

Back 77

> 1-D
> 2-D planar woven
> random orientation --> isotropic properties

Front 78

Definition: Interface

Back 78

Interface is between the primary and secondary phases in a composite material

Front 79

Definition: Interphase

Back 79

An interphase is like an adhesive layer that is added between the primary and secondary phases

Front 80

Variation in strength and stiffness for a composite

Back 80

non-linear as a function of direction relative to the longitudinal axis

Front 81

What is the tolerance of a system

Back 81

2* sigma

Front 82

Two approaches to quality control

Back 82

1) Inspect and Part rework (worse)
2) Continual Process Improvement (better)

Front 83

Quality Loss Function

Back 83

2*sigma = 4* cost

Front 84

what does k stand for in 2^k factorial design

Back 84

k refers to the number ofvariables being tested

Front 85

what is the 95% confidence interval

Back 85

2* sigma

Front 86

weight of carbon

Back 86

12 u

Front 87

weight of oxygen

Back 87

16 u

Front 88

weight of Nitrogen

Back 88

14 u

Front 89

Weight of Fluorine

Back 89

19 u