casting applications1
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Casting Processes
• Foundry (sand) Casting• Investment Casting
• Directional solidification and single crystal pulling
• Permanent mold casting (eg. ingots)
• Die Casting
• Squeeze casting
• Centrifugal casting
• Rapid solidification processes
(strip casting, spray for powder metallurgy, etc.)
• Continuous Casting
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Foundry Casting
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Foundry (sand) casting is:
• one of the oldest manufacturing processes
• 6th largest U.S. industry
• Advantages – Easy to produce complex shapes
– Inexpensive (especially for small quantities)
– Only way to produce brittle alloy parts
• Disadvantages – Energy intensive
– Pollution control problems
– Defects
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Inclusion-related defects in foundry
casting filling
Bubble trail
micro-graphs
J. Campbell & M. Jolly,Univ. Birmingham, UK
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Schematic of bubbles and bubble
trails during mold filling
Mold cavity
runner
Down-sprue
J. Campbell & M. Jolly, Univ. Birmingham, UK
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Oxide-inclusion stringers coating
dendrites
SEM image of oxide stringer from a
collapsed bubble-trail tubeM. Jolly, Univ. Birmingham, UK
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Oxide-inclusion stringers coating
dendrites“eggs under tissue paper”
M. Jolly, Univ. Birmingham, UK
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Die Casting
ASM Casting Handbook, 2009
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Die Casting
Counter-gravity low-
pressure die casting
High-pressure die casting
Heat transfer controlled by:
- Interface resistance (mainly)
-mold & casting too)
Advantages:
Disadvantages:Small size (porosity problems for larger parts)
High capital cost (for dies): large numbers only
Nonferous only (low temperature)
Fast, economic production
(>400 parts / hour)
Thin sections possible
More sound than foundry
Very low cost per part
ASM Casting Handbook, 2009
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Centrifugal Casting
Products: eg. roll, cast-iron pipe
Advantages:
Disadvantages:
Radially symmetric parts only
OK for ferrous alloys
Sound, fine grain size, low porosity
Macrosegregation
expensive
ASM Casting Handbook, 2009
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
RadiationHeating
Investment Casting
1. Wax pattern
2. Dip in ceramic slurry
5. Shake out
Finished casting3. Heat
(sinter ceramic and melt wax)4. Pour metal
“lost wax” process
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Investment Casting
• Often cast wax patterns for producing clusters of
several patterns at once)
• Applications: small, precision parts,
eg. Jewelry, dental work, air foils, etc.
• Advantages
– Intricate shapes, thin walls, no parting line
– Good dimensional tolerance, good surface finish
– Low startup cost
• Disadvantages – Small parts only (slow heat transfer)
– Small quantities (pattern used only once)
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Single Crystal Turbine Blades:
enable more efficient jet engines
Conventional
(fine grain) columnar
grains
Single
crystal
• Insert ceramic cores for inner spaces• Laser drill holes
• Air flow through blade creates boundary layer so blade surface
stays cooler than the surrounding gases
Directional solidification
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Why directional solidification?
• Engines operate more efficiently at high
temperature – materials limitation
• Low temperature TH < 0.3
– Grain boundaries tangle dislocations
– Increase strength with fine grains
• High temperature TH > 0.5
– Grain boundaries have higher creep
– Increase strength by avoiding grain boundaries
• Ceramics would be good blade material if low-
temperature fracture resistance was better
=()
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Investment casting
& directional solidification
InductionHeatingCoils
Water Cooled Chill Block
Slow Withdrawal
FurnaceColdZone
FurnaceHot Zone
SuperalloyMelt
RadiationBaffleTurbine Blades
PouringBasin
GrainSelector
RadiationHeating
RadiationCooling
CeramicShell(Mold)
Directional solidification
• avoid grain boundaries to
achieve high-temperature creep
resistance and strength
• Must avoid nucleation of new
grains
• Avoid cold liquid
• Cool very slowly, maintain steep
1-D temperature Gradient
• across mushy zone
• Baffle keeps top zone hot and
bottom cool, and high GYu et al, 1990
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Grain Defects in Single-Crystal
Castings (eg. turbine blades)
Secondary grain originated from grain selector
High / low angle grain boundar
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Single-crystal defects
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Microstructure of single-crystal Ni
superalloy (from turbine blade)
Top view Side view
Note: Grain defect:
Different angle of
primary dendrite
arms
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Directional Solidification Research
Vertical zone-melting process
-to study directional
solidification (dendrite growth,
etc.)
Also called:
“floating zone” or
“Bridgeman” process
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
consisting of alternating
plates of 2 different types
G/R maps to predict solidification structure
R =
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Kurz & Fischer Fig. 4.18
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
G/R maps to avoid crystal defects
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Freckle Formation - study
Ma et al
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Freckle
Formation map
(measured)
CMSX-4 nickel superalloy
Tliq = 1375 oC
20mm x 180mm rod samples
planar cellular Cellular/dendritic dendritic
equiaxed
Elements content, wt %Cr Co Mo Al Ti Ta Hf Re
Ni
6.5 9.0 0.6 5.6 1.0 6.5 0.1 3.0matrix
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Single Crystal Growing
• Eg. Single crystal growing of Si and
GaAs for semi-conductors
• Zone refining (purification)
• 1-D directional solidification processes:
– Bridgman process
– Czochralski
process
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Czochralski process
• Solidify onto an existing seed crystal
• “pull” very slowly out of melt to avoid:
– Dislocations (from thermal stress)
• Stabilize melt flow with electromagnetic force;
rotating crystal
• Product: Si or Ga-As semiconductors
Wikipedia, 2012
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Melt spinning
Spinning disk
plasma
Extremely high cooling rates > 106 oC/s
Nonequilibrium conditions and
microstrucctures
Large undercooling; amorphous metal
Product: rapidly quenched powder
Also achcieved by:
“spray atomization”
Purpose:
Wide range of unique properties and new
alloys:Eg. high-Si dissolved in Fe for transformers
Avoids segregation
Fine
powder
Inert atmosphere (He or
Ar)
Squeeze and sinter powder to net shape in furnace under pressure:
Hot Isostatic Pressing (HIP) “powder metallurgy
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Strip Casting:Rapid Solidification of Thin Metal Strip
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Rapid Solidification Processes
Single-wheel
melt spinning
(strip casting)Strip thickness variations, microstructure
From P. Steen, Cornell
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Other Rapid Solidification Processes
• Liquid metal droplet spraying(eg. OSPREY)
• 3-D Laser deposition(like rapid prototyping for metal)
• Rheocasting (slush casting)
• Welding(soldering, brazing, liquid-metal arc welding,
laser welding, etc)
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Semi-solid casting processes• Rheocasting
• Thixocasting
• Thixomolding (Mg)
• Often a raw-material for squeeze casting
• Expensive
• Very sound, no macrosegregation
High-quality die-cast parts
made from semi-solid
Microstructure of part
formed from semi-solid
ASM Casting Handbook, 2009
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Continuous Casting Process
Steel
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Steel continuous casting mold
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Continuous casting sub-mold
Courtesy Kawasaki Steel
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Defects in
Con. Casting
Surface defects from:
- Level fluctuations
- Meniscus freezing
- Poor flux infiltration
Internal defects from:
- Inclusions
- Flux entrainment
Cracks from:
- Thermal stress
- Bulging, etc.
- Metallurgical
embrittlement
Water
Spray
Longitudinal Section through Slab Caster
(not to scale)
Molten Steel Pool
Solidifying Steel Shell
Flux
Rim
Submerged Entry Nozzle
Support
Roll
Roll Contact
Ferrostatic
Pressure
Bulging
Roll
Nozzle
Nozzle
copper
mold
Liquid Flux
Air Gap
Flux Powder
jet
nozzle
portargon
bubbles
Inclusionparticles andbubbles
Resolidified
Flux
Contact
Resistances
Oscillation
Mark
entrainment
CL
B.G. Thomas
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.Courtesy of SMS
Thin slab caster
ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
R. O’Malley (Armco, Inc), D. Creech and B.G. Thomas (Univ. of Illinois)
5.2” Thin Slab Caster
(Armco Mansfield)Physical Water Model and
Computer Simulation
Continuous Casting of Steel
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ME 550 – Lecture 1 © 2005 Brian G. Thomas, University of Illinois at Urbana-Champaign, All Rights Reserved.
Choose a casting process for each product.
• a) cast iron engine blocks for tractors
• b) 5 large aluminum ashtrays
• c) 500,000 aluminum ashtrays
• d) a gold wedding ring with intricate detail.
• e) a life-size bronze statue of the President
• f) a single crystal turbine blade (airfoil)
• g) many stainless steel sheets for stamping and
forming into car mufflers
• h) 5 steel crank shafts
• i) 500,000 steel crank shafts
• j) steel rails (for railroad tracks)
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