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Processing Metals (Ch. 6)

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Expendable Mold Casting

Molds made out of plaster, sand, ceramics that are combined with binders.The mold is broken up to remove the part.

Non-Expendable Mold Casting

Mold is designed to be used repeatedly

Expendable Mold: Sand Casting

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Floor and Pit casting = sand casting of large components (on the floor)or very large parts using a pit as the drag

Loam molding = for HUGE castings. 50% clay, 50% sand is smoothed over substrate made of bricks, wood …whatever to make contour, sheet metal sweeps used

Shell Molding = Sand glued with a resin: phenol formaldehydes, urea formaldehydes, polyesters etc sand can be reclaimed(good surface finish, can be automated, expensive)

CO2 process (works with sands containing 3-5% sodium silicate)

· · → ·

Plaster Molds – No ferrous alloys …Ag, Au, Mg, Cu, Al etc allowed

Unicast – Plaster is poured over pattern and partially cured, pattern removed and mold is fired in furnace

Osborn-Shaw process – aggregate, hydrolyzed ethyl silicate, alcohol poured over pattern, slurry hardens to rubbery state, and lit on fire causing volatiles to burn off leaving ceramic with microcracks, crating pourous mold

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Investment Casting

Cast parts

Figure 6.2

Permanent Mold Casting

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Continuous Casting

Working Process

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Hot Rolling of Steel

Cold Rolling of Metal Sheet

Figure 6.8

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Effects of Plastic Deformation

Extrusion

Container

Metal

Container

Metal

Die

DirectExtrusion

indirectExtrusion

Figure 6.9

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Extrusion details

Forging

Direct Forging

Indirect Forging

Dies

Metal

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Drawing

Wire or rod

Carbide nib

Figure 5.13

Figure 6.14

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Mechanical Properties

Strong

Weak

Tough

Brittle

Hard

Soft

Tensile test

SpecimenExtensometer

Load Cell

Figure 6.18

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Modulus of Elasticity

Yield Strength

Stress vs Strain

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Examples Stress vs Strain

Figure 6.14

Stress-strain curves of different metals

True Stress – True Strain

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Yield Strength

Figure 6.23

Poison’s Ratio

Shear Stress

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Percent elongation

Ductility

Percent Reduction in Area

Hardness and Hardness Testing

Figure 6.27Rockwell hardnesstester

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Hardness Tests

Table 6.2

Rockwell Details

Scale IndenterMajor LoadF1N

E Applications

A 120oDiamond cone 490.5 100 Sheet steel ; shallow case hardened

B 1/16" steel ball 882.9 130 Copper, Aluminium alloys, Low Carbon Steel

C 120oDiamond cone 1373.4 100 Most Widely Used -Hardened Steels, Cast irons etc

D 120oDiamond cone 882.9 100 Thin but hard steels, Ductile Iron (Pearlitic

E 1/8" steel ball 882.9 130 Cast Iron, Aluminium, Bearings alloys

F 1/16" steel ball 490.5 130 Annealed copper alloys , Soft thin metals

G 1/16" steel ball 1373.4 130 Phosphor bronze, beryllium copper, malleable irons, Lead etc

H 1/8" steel ball 490.5 130 Soft Metals Plastics etc

K 1/8" steel ball 1373.4 130 Soft bearing metals, Plastics, soft materials.

L 1/4" steel ball 490.5 130 Soft bearing metals, Plastics, soft materials.

M 1/4" steel ball 882.9 130 Soft bearing metals, Plastics, soft materials.

P 1/4" steel ball 1373.4 130 Soft bearing metals, Plastics, soft materials.

R 1/2" steel ball 490.5 130 Soft bearing metals, Plastics, soft materials.

S 1/2" steel ball 882.9 130 Soft bearing metals, Plastics, soft materials.

V 1/2" steel ball 1373.4 130 Soft bearing metals, Plastics, soft materials.

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Plastic Deformation in Single Crystals

Figure 6.28

Slip bands

Zinc single crystal

Slip Mechanism

Dislocation cell structure in lightlydeformed Aluminum

Figure 5.33

Figure 5.32

Wall of high dislocation density

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Slip in Crystals

Close packedplane

Non-close-packedplaneFigure 5.34

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Critical Resolved Shear Stress

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1A

Frr

Slipdirection

Normal toSlip plane

0A

F

A1=Area ofSlip plane

Schmid’s Law

Example: Calculate on BCC Iron’s 112 111 slip system with 11.7 MPaapplied in the [001] direction.

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a

a

[112]

2

[001]

tan 22

→ 35.26

a

[111]

2

[001]

tan 2

→ 57.4

Twinning

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Twinning

Hall Petch Equation

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Effects of Grain Boundaries on Strength

Figure 6.40 Figure 6.40 Figure 6.40Stress-strain curve of singleand polycrystalline copper

Slip bands in polycrystallinealuminum grains

Dislocations piled up against grain boundaries in stainless steel

Effect of Cold Work on Tensile Strength

Stress-Strain curves of 1018 steel

1018-Cold Rolled

1018-Annealed

Figure 5.45

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Recovery

Cold worked (lots ofdislocations)

Recovered (dislocationsmoved to low-energy configuration)

T < Tcrystallization

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Recrystallization

85% cold rolled

Annealed 316C 1 hr

Stress relieved 302C 1 hr

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Temperature and Time

Mechanism of Superplasticity

Grains before and after deformation