1. MSE 440/540: Processing of Metallic Materials
Instructors: Yuntian Zhu
Office: 308 RBII
Ph:
Lecture 3: Casting I,
Text book,
Office hour, by appointment
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2. Casting process
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3. USS New York LPD 21
Built from 24 tons of scrap steel from the World Trade Center
The steel was melted down in a foundry in Amite, LA to cast the ship’s bow section. When it was poured into the molds on Sept 9, 2003, “those big rough steelworks treated it with total reverence”, recalled Navy Capt. Kevin Wensing.
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4. Our focus here is relatively small parts
Advantages:
Can create complex part geometries
Can produce net-shape parts
Cheap
Disadvantages :
Limitations on mechanical properties
Poor dimensional accuracy and surface finish for some processes; e.g., sand casting
Safety hazards to workers due to hot molten metals
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5. Open Molds and Closed Molds
Two Categories of Casting Processes
Expendable mold processes – one time use
Mold materials: sand, plaster, and similar materials, plus binders
Permanent mold processes – multiple use
Made of metal (or, less commonly, a ceramic refractory material)
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6. Sand Casting Mold
Definition: Cope, Drag, parting line, riser, runner, cavity, core,
downsprue
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7. Cooling Curve for a Pure Metal
A pure metal solidifies at a constant temperature equal to its freezing point (slightly below melting point)

8. Riser
Reservoir in the mold which is a source of liquid metal to compensate for shrinkage of the part during solidification
The riser must be designed to freeze after the main casting in order to satisfy its function
To minimize waste in the unit operation, it is desirable for the volume of metal in the riser to be a minimum
Since the shape of the riser is normally designed to maximize the V/A ratio, this allows riser volume to be reduced to the minimum possible value
Quiz: why do we want to maximize the V/A ratio?

9. Solidification of Pure Metals
Due to chilling action of mold wall, a thin skin of solid metal is formed at the wall surface immediately after pouring
Grain structure in a casting of a pure metal, showing randomly oriented grains of small size near the mold wall, and large columnar grains oriented toward the center of the casting

10. Solidification of Alloys
Most alloys freeze over a temperature range
Phase diagram for a copper‑nickel alloy system and cooling curve for a 50%Ni‑50%Cu composition
Quiz: any problem with this cooling curve?

11. Solidification of Alloys
Characteristic grain structure in an alloy casting, showing segregation of alloying components in center of casting

12. Cellular and Dendritic Solidification
Constitutional Supercooling:
Cell Structure:
Dendritic structure:
Condition for non-constitutional cooling (Planar): T T1 T2 T3 TE XS XL X0 XE
Quiz: Constitutional cooling lead to the unstability of flat interface, cell formation
D/v =characteristic width of the concentration profile
Page 214, figure 4.22
Cooling starts at T1, but stops at T3 where it behaves like a pure metal with T no longer decreasing until the end
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13. No Diffusion in Solid, Diffusional Mixing in Liquid
D/v = Characteristic width of concentration profile
Fig. 4.22, T T1 T2 T3 TE XS XL X0 XE
At T3, solid T,
D/v = characteristic width of the concentration profile
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14. Solidification Time
Total solidification time tTS = time required for casting to solidify after pouring
tTS depends on size and shape of casting by relationship known as Chvorinov's Rule
where V = volume of the casting; A = surface area of casting; n = exponent with typical value = 2; and Cm is mold constant.
Quiz: how to get fast cooling

15. Shrinkage during Solidification and Cooling

16. HW Assignment Read Chapter 6 HW: Example 5.2 on page 109
Problems 5.8, 5.9, 5.11, 5.12, 5.13,5.16
Quiz for online students: why the columnar structure grow perpendicular to the mold wall? (submit it directly to Dr. Zhu by
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