Final Exam Review
Material-Process-Geometry Relationships
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Function
Process
Material Geometry
Role of Prod Engr
Role of Mfg Engr
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Materials in Manufacturing
Most engineering materials can be classified into one of four basic categories: 1. Metals
2. Ceramics
3. Polymers
4. Composites
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Processing Operations
Three categories of processing operations:
1. Shaping operations - alter the geometry of the starting work material
2. Property‑enhancing operations - improve physical properties of the material without changing its shape
3. Surface processing operations - clean, treat, coat, or deposit material onto the exterior surface of the work
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Shaping – Four Main Categories
Solidification Processes - starting material is a heated liquid that solidifies to form part geometry
Deformation Processes - starting material is a ductile solid that is deformed
Material Removal Processes - starting material is a ductile/brittle solid, from which material is removed
Assembly Processes - two or more separate parts are joined to form a new entity
Comparing Processes
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Stress-Strain Relationships
Figure 3.3 Typical engineering stress‑strain plot in a tensile test of a metal.
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True Stress-Strain Curve
Figure 3.4 ‑ True stress‑strain curve for the previous engineering stress‑strain plot in Figure 3.3.
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Strain Hardening
Figure 3.5 True stress‑strain curve plotted on log‑log scale.
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Recrystallization and Grain Growth
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Scanning electron micrograph taken using backscattered electrons, of a partly recrystallized Al-Zr alloy. The large defect-free recrystallized grains can be seen consuming the deformed cellular microstructure.
--------50µm-------
Phase Dispersion – speed of quenching
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Allotropic Transformation and Tempering
Figure 6.4 Phase diagram for iron‑carbon system, up to about 6% carbon.
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Tempered Martensite
Austenizing
Quenching
Figure 27.5 Precipitation hardening: (a) phase diagram of an alloy system consisting of metals A and B that can be precipitation hardened; and (b) heat treatment: (1) solution treatment, (2) quenching, and (3) precipitation treatment.
Precipitation Hardening - Al 6022 (Mg-Si)
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Machining Relationships
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Machine Tool
Workpiece
Workholding Tool Cutting Tool
Higher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperature
Figure 21.12 Effect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation
Effect of Higher Shear Plane Angle
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Turning Parameters Illustrated
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Machining Calculations: Turning
Spindle Speed - N (rpm) v = cutting speed Do = outer diameter
Feed Rate - fr (mm/min -or- in/min) f = feed per rev
Depth of Cut - d (mm -or- in) Do = outer diameter
Df = final diameter
Machining Time - Tm (min) L = length of cut
Mat’l Removal Rate - MRR (mm3/min -or- in3/min)
oDπ
vN
2fo DD
d
rm f
LT
fNfr
dfvMRR
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Unit Power in Machining
Useful to convert power into power per unit volume rate of metal cut Called the unit power, Pu or unit horsepower, HPu
or
Tool sharpness is taken into account multiply by 1.00 – 1.25 Feed is taken into account by multiplying by factor in Figure 21.14where MRR = material removal rate
MRRP
P cu
MRRHP
HP cu
What if feed changes?
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Unit Horsepower
The significance of HPu is that it can be used: 1) to determine the size of the machine tool required to perform a particular cutting operation; and 2) the size of the cutting force on the workholding and cutting tools.
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E
MRRCHP
E
HPHP
v
MRRCHP
v
HPF
MRRCHPHP
fucg
fucc
fuc
000,33000,33
HPu ~ hp/in3/min
Cf ~ correction factor
MRR ~ in3/min
Fc ~ lb
V ~ ft/min
E ~ machine tool efficiency
33,000 ~ conversion between ft-lb & hp
Example
In a turning operation on stainless steel with hardness = 200 HB, the cutting speed = 200 m/min, feed = 0.25 mm/rev, and depth of cut = 7.5 mm. How much power will the lathe draw in performing this operation if its mechanical efficiency = 90%.
From Table 21.2, U = 2.8 N-m/mm3 = 2.8 J/mm3
Since feed is 0.25 mm/rev, the correction factor is 1
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Example: Solution
MRR = vfd
= (200 m/min)(103 mm/m)(0.25 mm)(7.5 mm)
= 375,000 mm3/min = 6250 mm3/s
Pc = (6250 mm3/s)(2.8 J/mm3)(1.0) = 17,500 J/s
= 17,500 W = 17.5 kW
Accounting for mechanical efficiency, Pg
= 17.5/0.90 = 19.44 kW
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Flow of Molten Liquid Requires Heating
Heat Transfer of Liquid in Mold Cavity During and After Pouring
Solidification into Component
Casting
Common process attributes:
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Gating System
Channel through which molten metal flows into cavity from outside of mold
Consists of a downsprue, through which metal enters a runner leading to the main cavity
At top of downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue
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Pouring Calculations
Minimum mold filling time, MFT
MFT =V/Q
Q: volumetric flow rate, cm3/s
V: mold cavity volume, cm3
Chvorinov's Rule
where TST = total solidification time; V = volume of the casting; A = surface area of casting; n = exponent usually taken to have a value = 2; and Cm is mold constant
n
m A
VCTST
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Amount and Composition
Figure 6.2 Phase diagram for the copper‑nickel alloy system.
Shrinkage in Solidification and Cooling
Figure 10.8 Shrinkage of a cylindrical casting during solidification and cooling: (0) starting level of molten metal immediately after pouring; (1) reduction in level caused by liquid contraction during cooling (dimensional reductions are exaggerated for clarity).
Shrinkage in Solidification and Cooling
Figure 10.8 (2) reduction in height and formation of shrinkage cavity caused by solidification shrinkage; (3) further reduction in height and diameter due to thermal contraction during cooling of solid metal (dimensional reductions are exaggerated for clarity).