Casting - erranjitsingh.weebly.comerranjitsingh.weebly.com/uploads/3/9/1/6/391693/casting.pdf · –sand casting - as large as you like –small - 1 mm or so •Tolerances –0.005

ME 4210: Manufacturing Processes and Equipment

Prof. J.S. Colton © GIT 2011

1

Casting Processes

ver. 2



2

Types of Parts Made

• Engine blocks

• Pipes

• Jewelry

• Fire hydrants



3

Complex, 3-D shapes

• Near net shape

• Low scrap

• Relatively quick process

• Intricate shapes

• Large hollow shapes

• No limit to size

• Reasonable to good surface finish



4

Processes

• Sand

• Shell

• Plaster

• Ceramic

• Investment

• Lost foam

• Pressure

• Vacuum

• Die

• Centrifugal

• Squeeze

• Semi-solid

• Single crystal

• Directional

solidification

• Slush

• Continuous



5

Metals processed by casting

• Sand casting – 60%

• Investment casting – 7%

• Die casting – 9%

• Permanent mold casting – 11%

• Centrifugal casting – 7%

• Shell mold casting – 6%



6

Breakdown of Castings

• Ingots for bulk deformation processing -

85%

• Cast to near net shape - 15%



7

Ingots

• Iron or steel molds

• Water-cooled molds

• Continuous casting



8

Shapes

• Expendable Molds

– sand

– shell

– slurry

– investment

• lost wax

• lost foam

• Permanent mold

(cavity)

– die casting

– hot chamber

– cold chamber



9

Shapes

• Centrifugal

– pipes

– spinning



10

Capabilities

• Dimensions

– sand casting - as large as you like

– small - 1 mm or so

• Tolerances

– 0.005 in to 0.1 in

• Surface finish

– die casting 8-16 micro-inches (1-3 mm)

– sand casting - 500 micro-inches (10-25 mm)



11

Casting Steps quick route from raw material to finished

product

• Melt metals

• Pour / force liquid into hollow cavity

(mold)

• Cool / Solidify

• Remove

• Finish



12

Melting

• Raw material (charge)

– scrap, alloying materials

• Atmosphere

– Air (oxygen), vacuum, inert gas (argon)

• Heating

– External - electric, gas, oil

– Internal - induction, mix fuel with charge • steel making in blast furnace -mix coke with iron

• Furnace material

– refractory ceramics

Heat

Raw materials

Furnace

Atmosphere



13

Furnaces

Blast furnace Basic Oxygen Furnace



14

Furnaces

Electric Arc Furnace

Oxygen-Fuel,

Oxygen Lance Furnace



15

Furnaces

Induction Furnace Electric Furnace



16

Sand Casting



17

Sand Casting



18

Sand Casting



19

Sand Casting Steps



20



21

Sand Cast Parts



22

Permanent Mold Casting



23

Low Pressure Casting



24

Die Casting (high pressure)



25

Die Casting Machine



26

Die Casting

Cold chamber

Hot chamber



27

Direct Squeeze Casting



28

Die Casting Part Example



29

Continuous Casting



30



31



32



33

Investment

Casting



34

Vacuum Casting



35

Investment (top) and Conventional

Castings



36

Lost Foam Casting



37

Lost Foam Castings



38

Centrifugal Casting

vertical sand-lined mold

casting

horizontal



39

Centrifugal Casting



40

Pipe Casting

Process



41

Directional Solidification



42

Casting Characteristics Table 5.6

Typical Weig ht (kg)

Typical

surface

Section

thickness (mm)

Process

materials

cast Minimum Maximum

finish

(micron,

Ra) Porosity*

Shape

complexity

*

Dimensional

accuracy* Minimum Maximum

Sand All 0.05 No limit 5-25 4 1-2 3 3 No limit

Shell All 0.05 100+ 1-3 4 2-3 2 2 --

Expendable

mold

pattern All 0.05 No limit 5-20 4 1 2 2 No limit

Plaster

mold

Nonferrou

s (Al, Mg,

Zn, Cu) 0.05 50+ 1-2 3 1-2 2 1 --

Investment

All

(High melting

pt.) 0.005 100+ 1-3 3 1 1 1 75

Permanent

mold All 0.5 300 2-3 2-3 3-4 1 2 50

Die

Nonferrou

s (Al, Mg,

Zn, Cu)



43

Microstructure



44

Microstructure - Dendrites

• Finer structure at

walls

• Grains / dendrites

grow to center



45

Grains on Willie B’s head



46

Microstructure - Dendrites



47

Fluidity



48

Casting Defects - Porosity



49

Casting Defects



50

Shrinkage

TABLE 5.1

Metal or alloy

Volumetric

solidification

contraction (%) Metal or alloy

Volumetric

solidification

contraction (%)

Aluminum 6.6 70%Cu–30%Zn 4.5

Al–4.5%Cu 6.3 90%Cu–10%Al 4

Al–12%Si 3.8 Gray iron Expansion to 2.5

Carbon steel 2.5–3 Magnesium 4.2

1% carbon steel 4 White iron 4–5.5

Copper 4.9 Zinc 6.5

Source: After R. A. Flinn.



51

Differential Cooling

• Transition between thicker and thinner

sections can lead to porosity



52

Pipe Defect

• Due to shrinkage giving rise to

a funnel-like cavity

• Solutions

– insulate top (glass wool)

– heat top (exothermic mixture -

thermit)



53

Defects - Hot Tears



54

Chills

Car Rims



55

Stamped Cast



56

Casting Defects - Porosity



57

Design Rules Summary

• Uniform wall thickness

• Flat parting lines

• Gradual thickness

transitions

• Draft for removal

– tapers: 0.5 to 2 degrees

• Surface of mold gives

surface of part



58

Sand Casting Rules



59

Casting costs

TABLE 5.10

Cost*

Process Die Equipment LaborProductionrate (Pc/hr)

Sand L L L–M



60

Process economics



61

Documents

Casting - erranjitsingh.weebly.comerranjitsingh.weebly.com/uploads/3/9/1/6/391693/casting.pdf · –sand casting - as large as you like –small - 1 mm or so •Tolerances –0.005