ACE305: Aircraft Components Design and Manufacture Lec 3

Process
Engineers
Process
Engineers Tool
Engineers
Tool
Engineers Standarts
Engineers
Standarts
Engineers
Material
Handling
Engineers
Material
Handling
Engineers
Quality
Control
Engineers
Quality
Control
Engineers
Facility
Engineers
Facility
Engineers
Manufacturing EngineersManufacturing Engineers
Application of science, engineering, technology, and
economics to manufacture products of a quality, quantity,
and cost competitiveness in the market place.
Manufacturing Engineering
1.11
Page 1
ACE 305: Dr Mohamed Elfarran
2020
Spectrum of Specialization
Page 2

 Assembly process
 Plant capabilities
 Existing equipment
Process Engineers
Develop a logical sequence of manufacturing operations
for each assembly and for the final assembly of all sub-
assemblies into a finished product. Need a detailed
knowledge of
 Forming process
 Machining process
1.12
Page 2
2020
Page 3

Provide proper tools for manufacturing.
Following tools are commonly used in
manufacturing industry:
 Conventional Tools
 Standard tools: Cutting tools, dies
 Non-standard tools: Workpiece holding
devices
 Non-traditional Tools
 Electro-discharge machining (EDM):
electrodes
 Laser
Tool Engineers
1.13
Page 3
2020
Page 4

Standards Engineers
Synchronize the entire manufacturing process. For this
purpose, they determine the time requirement for each
operation and their sequences utilizing work standards
and standard times.
1.14
Page 4
2020
Page 5

Material Handling Engineers
 Plans for efficient transfer of
materials from one point to
another. They must avoid the
following:
 Disruption of production due to
lack of batches
 Unnecessary level of in-process
stock
 High degree of congestion
1.15
Page 5
2020
Page 6

Facility Engineers
 Provide efficient equipment
layout. They must avoid the
following:
 Higher material handling
cost
 Longer manufacturing time
 High level of in-process
stock
 High degree of congestion
in the process flow.
 In some cases, facility
engineers and material
handling engineers combine
in a single group called plant
engineers.
1.16
Page 6
2020
Page 7

Quality Control Engineers
Maintain the described level of
product quality by employing a
quality assurance system. Quality
can be established at:
 Product design stage
 Design stage of production system
 Production stage by inspection.
1.17
Page 7
2020
Page 8

 Quality is defined at the design stage and is built
into the product during manufacturing.
 Design quality sets the specifications on the material
and tolerances.
 Manufacturing quality is the degree of comformity to
the design specifications.
1.18
Page 8
2020
Manufacturing Quality
Page 10

Quality vs. Cost
Quality ↑ Cost ↑ Demand ↓
Quality ↑ Quantity ↓ Cost ↑
1.19
Page 9
2020
Page 11

Manufacturing Quality (2)
Low Reliability
Good
Enough
High Reliability
High CostLow Cost
Quality Level
CostandValue
Good
Enough
Value to
customer
Cost to
customer
Quality Level
CostandValue
Good
Enough
Total
cost
Original
cost
Running
cost
1.20
Page 10
2020
Page 12

Creation of
Cohesion
Maintenance of
Cohesion
Destruction
of Cohesion
Increase of
Cohesion
Shape (Form) Modification
2. Deforming 3. Seperating 4. Joining
6. Changing Material Properties
1. Primary
Forming
Rearrangement
of Particles
Removal of
Particles
Addition of
Particles
5. Coating
1.21
Page 11
2020
Classification of Manufacturing
Processes (DIN 8530)
Page 14

Manufacturing Processes
1. Primary Forming: Casting, powder metallurgy
2. Deforming: Metal forming processes (bulk and sheet
forming)
3. Separating: Machining
• Conventional machining (turning, milling, grinding, etc.)
• Non-traditional machining (EDM, ECM, EBM, LBM, etc.)
4. Joining: Welding, brazing, riveting, etc.
5. Coating: Painting, electroplating, etc.
6. Changing Material Properties: Heat treatments.
1.22
Page 12
2020
Page 15

Molecular Structure
 Primary bonds: Strong atom-to-atom attractions by
exchange of valence electrons.
 Ionic bond
 Covalent bond
 Metalic bond
 Secondary bonds: Weak attraction between molecules
(van der Waals forces)
 Permanent Dipole Bond
 Fluctuating Dipole Bonds
2.1
Page 13
2020
Page 17

Ionic Bonds
Large inter-atomic forces are created by the “Coulomb”
effect produced by positively and negatively charged ions.
2.2
Page 14
2020
Page 18

Covalent Bonds
 Large inter-atomic forces are
created by the sharing of
electrons to form directional
bonds.
 The atoms have small
differences in electro-
negativity & close to each
other in the periodic table.
2.3
Page 15
2020
Page 19

Metalic Bonds
Atoms loose their outer
shell electrons and
become (+) ions
surrounded by free
electron cloud. Free
electrons act like “cement”
to hold atoms together.
2.4
Page 16
2020
Page 20

Properties
Property Ionic Bond Covalent Bond Metalic Bond
Hardness High Low → Very High Low → High
Ductility Brittle Brittle Ductile
Melting
Temperature
High Low → Very High Low → High
Electrical and
Thermal
Conductivity
Low Low High
Page 17
2020
Page 21

Crystaline Structure
Body Centered
Cubic (BCC)
Face Centered
Cubic (FCC)
Hexagonal Closed
Packed Cubic (HCP)
[*] Adapted from Groover (1996).
Page 18
2020
Page 22

Structures of Common Metals*
BCC Chromium (Cr), Iron (Fe), Molybdenum (Mo),
Tantalum (Ta), Tungsten (W)
FCC Aluminum (Al), Copper (Cu), Gold (Au), Lead
(Pb), Silver (Ag), Nickel (Ni)
HCP Magnesium (Mg), Titanium (Ti), Zinc (Zn)
[*] At room temperature (20oC).
Page 19
2020
Page 23

2020
Uniaxial Tension Experiment
Page 25

Stress and Strain
0A
P
eng =σ
0
0

 −
=engε
where P is load; A0 refers to initial
(undeformed) area.
Hooke’s Law (Elastic Region):
engeng E εσ ⋅=
Proportional Limit
Fracture Strength
Ultimate Strength
Yield Strength
Elastic Region Plastic Region
STRAIN (ε )eng
0.2% offset
or
0.002 (mm/mm)
Engineering Stress - Engineering Strain Curve
Uniform
Elongation Necking Fracture
Engineering stress:
Engineering strain:
Page 37
2020
Page 26

Stress and Strain (2)
Strain (ε, εeng)
Stress(σ,σeng)
x
x
σ,ε curve
σeng, εeng curve
yield stress
True Stress:
A
P
=σ
True Strain Increment:

d
d =ε
True Strain (Total):






== ∫ 0
ln
0






d
ε
Page 38
2020
Page 27

Additive Property of True Strain
Assume that a specimen of length l0 is elongated to l1
then to l2:






=→
0
2
20
ln


ε 





⋅=→
0
1
1
2
20
ln




εor






+





=→
0
1
1
2
20
lnln




ε hence
211020 →→→
+= εεε
Page 39
2020
Page 28

Example 1
 A uniform bar of 100 mm initial length is
elongated to a length of 200 mm in three
stages:
 Stage 1: 100 mm to 120 mm
 Stage 2: 120 mm to 150 mm
 Stage 3: 150 mm to 200 mm.
 Calculate the engineering and true strains for
each stage and compare the sums of the
three with the overall values of the strains.
Page 40
2020
Page 29

Strain Relationships
Constant volume during plastic deformations implies:






≈





=⇒≈→⋅≈⋅
A
A
A
A
AA 0
00
0
00 lnln




 ε
Relationship between true and engineering strains:
( )engengeng εεε +=





→+=→−=
−
= 1lnln11
0000
0








Hence ( ) 11ln −=+= ε
εεε eengeng or
Page 41
2020
Page 30

Stress Relationships (Cont’d)
Relationship between true and engineering stresses:
0
0
0 

eng
A
A
A
P
A
P
σσ ≈⋅== 





+
−
≈ 1
0
0


engσσ
with
0
0

 −
=engε
We obtain: ( ) ε
σσεσσ eengengeng ≈+≈ or1
or
Page 42
2020
Page 31

b
a c
d
e
g
h
f
Load
Strain, εeng
When metals are plastically
deformed, their strength increase.
This is called strain- or work
hardening.
Power (Ludwik or Hollomon)
Law for the flow curve:
n
plf Kεσ =
where
K, n are material constants.
n is called strain hardening
exponent.
Page 43
2020
Strain Hardening
Page 32

Strain Hardening (Cont’d)
AP f ⋅= σ
0=⋅+⋅= dAdAPd ff σσnecking
const.=⋅= AV
εdA
d
AdAdAdAdV ⋅−=⋅−=→=⋅+⋅=


 0
εσ
ε
εεσεσ d
n
dKndK f
n
f
n
f ⋅⋅=⋅⋅⋅≈→⋅≈ −1
0=⋅−⋅⋅= εσεσ
ε
dd
n
Pd
u
necking un ε=∴
(1)
(2)
(3)
Page 44
2020
Page 33

(Cold) Flow Curves
Courtesy of Prof. Erman Tekkaya
Page 45
2020
Page 34

Ductility is the ability to deform
without damage.
Elongation is not uniform after necking.
Engineering “strain” at fracture:
0
0

 −
= fracfrac
engε
Another measure of ductility is the reduction of
area measured on the fractured test piece:
0
0
A
AA
q frac−
=
l
Necking
Ductility
Page 46
2020
Page 35

b
a c
d
e
g
h
f
Load
Strain, εeng
Assume material is cold worked to
point “d”:
c
d
c
A
P
YS =
For small elastic strains: Ac ≈ Ad
n
d
d
dd
flow K
A
P
εσ ⋅≈=
n
d
d
flowc KYS εσ ⋅≈≈∴
Yield Strength
Page 47
2020
Page 36

b
a c
d
e
g
h
f
Load
Strain, εeng
Cold Worked Material:
c
ec
A
P
UTS =
Annealed Material:
a
ea
A
P
UTS =
( ) ( )
c
aac
A
A
UTSUTS ⋅= annealedhardenedwork
Ultimate Tensile Strength
Page 48
2020
Page 37

Effects of Cold Work
Page 49
2020
Page 38

For wire drawing, the equivalent
plastic strain is defined as
Since
Flow stress (~ yield strength) of the
drawn-wire becomes
Equivalent Strain – Wire Drawing
Page 55
2020
Page 39

Example 3
The strain hardening behavior of an annealed
low-carbon steel is σ = 700⋅ε0.3 [MPa]. The bar
made from this metal is initially cold worked by
10%, followed by an additional cold work of 15%.
 Determine the probable yield strengths
 Find the (ultimate) tensile strengths of the bar for the
initial- and final case.
 If the ductility of the annealed material is 50%,
calculate the ductility for each case.
Page 56
2020
Page 40

 Hot working is performed at TH > 0.5.
 Restoration and slip processes occur simultaneously.
 Hot working is strain-rate sensitive as
dt
d
C m
f
ε
=εε=σ  ,)(
 The strain-rate sensitivity exponent m takes the following values:
 Cold working: -0.05 < m < 0.05
 Hot working: 0.05 < m < 0.30
 Super-plasticity: 0.30 < m < 0.70 (very fine grain metals)
 Higher the value of m the larger the elongation.
Hot Working
Page 60
2020
Page 41

(Warm/Hot) Flow Curves
Courtesy of Prof. Erman Tekkaya
Page 61
2020
Page 42

Annealing is the process of heating a material to some
elevated temperature, holding it at that temperature,
and cooling it back to room temperature.
Annealing is applied to:
 Reduce hardness and brittleness (recovery)
 Recrystallize cold worked metals and obtain a specific
microstructure (recrystallization)
 Relieve residual stresses induced by prior shaping
processes (stress relief annealing)
Page 62
2020
Definition of Annealing
Page 43

Annealing
Although the cold-worked
dislocation cell structure is
mechanically stable, it is
NOT thermodynamically
stable!
Recovery Annealing:
No change in grain structure,
just rearrangements of
dislocations
Primary Recrystallization:
New grains are built at nuclei
produced by cold working
Secondary Recyrstallization:
Grain growth by coalescence of
grains. Hydrogen embrittlement
leads to a decrease in ductility.
Page 63
2020
Page 44

Annealing (2)
Time and temperature
have interchangeable
effects!
Page 64
2020
Page 45

Annealing (3)
 Recyrstallization can
occur only with nuclei
produced by cold
working.
 The more the prior cold
work, the more the
nuclei and the smaller
the grain size.
 If there is no prior cold
work, there will be no
recyrstallization at all.
Page 65
2020
Page 46

σxx
σxx
τyx
σyyσyy
τxy
x
y
z
τxz
σzz
σzz
τyz
τzy
τzx
General 3-D State of
Stress:
σ1
σ1
σ2
σ2
σ3σ3
σ1 >σ 2 >σ 3
Principal State of
Stress:
Independent Cartesian Stress Components:
σxx, σyy, σzz, τxy, τyz, τzx
Stress States
Page 66
2020
Page 47

Stress States (Cont’d)
σxx
σxx
τyx
σyy
σyy
τxy
x
y
z
x
y
σyy
σyy
τyx
σxxσxx
τyx
τxy
τxy
Plane Stress
State:
Uniaxial Stress
State:
σxx
σxx
x
y
σxxσxx
Page 67
2020
Page 48

Transformation of Stress States:
Mohr’s Circle
Page 68
2020
Page 49

Uniaxial Yield Criterion:
Generalized Yield Criteria:
Tresca’s
Yield Criterion:
von Mises
Yield Criterion:
YSx =σ
k=
−
=
2
31
max
σσ
τ YS=− 31 σσ
( ) ( ) ( )[ ] YSeq =−+−+−=
2
13
2
32
2
21
2
1
σσσσσσσ
or
Yielding starts if
Yield Criteria
Page 69
2020
Page 50

ACE305: Aircraft Components Design and Manufacture Lec 3

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