Transcript Document 7556148

Final Exam Review
Material-Process-Geometry Relationships
Role of Prod
Engr
Function
Material
Geometry
Process
2
Role of Mfg
Engr
Materials in Manufacturing

Most engineering materials can be classified
into one of four basic categories:
1.
2.
3.
4.
3
Metals
Ceramics
Polymers
Composites
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
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
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
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-------
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Phase Dispersion – speed of quenching
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Allotropic Transformation and Tempering
Austenizing
Quenching
Figure 6.4 Phase diagram
for iron-carbon system, up
to about 6% carbon.
Tempered
Martensite
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Precipitation Hardening - Al 6022 (Mg-Si)
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.
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Machining Relationships
Machine Tool
Workholding Tool
Cutting Tool
Workpiece
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Effect of Higher Shear Plane Angle
 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
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Turning Parameters Illustrated
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Machining Calculations: Turning

Spindle Speed - N



Feed Rate - fr



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Do = outer diameter
Df = final diameter
Machining Time - Tm


f = feed per rev
Depth of Cut - d


v = cutting speed
Do = outer diameter
L = length of cut
Mat’l Removal Rate - MRR
v
N
π Do
fr  N f
Do  Df
d
2
L
Tm 
fr
MRR  v f d
(rpm)
(mm/min -or- in/min)
(mm -or- in)
(min)
(mm3/min -or- in3/min)
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
Pc
Pu 
MRR
HPc
HPu 
or
MRR
where MRR = material removal rate
 Tool sharpness is taken into account multiply by 1.00 – 1.25
 Feed is taken into account by multiplying by factor in Figure
21.14
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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.
HPc  HPu  C f  MRR
33,000  HPc 33,000  HPu  C f  MRR
Fc 

v
v
HPc HPu  C f  MRR
HPg 

E
E
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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


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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 Nm/mm3 = 2.8 J/mm3

Since feed is 0.25 mm/rev,
the correction factor is 1
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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Casting
Common process attributes:
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
Flow of Molten Liquid
Requires Heating

Heat Transfer of Liquid in
Mold Cavity During and
After Pouring

Solidification into Component
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
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Chvorinov's Rule
V 
TST  Cm  
 A
n
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
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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).