* Initial thickness to = 25 mm
* Final thickness tf = 20 mm
* Draft d = to - tf = 25 - 20 = 5 mm
* Roll radius R = 300 mm
* Roll rotational speed N = 100 rpm
* Strip width w = 200 mm
* Average stress Yavg = 140 MPa
* Roll contact length L = √(Rd) = √(300×5) = 30 mm
* Rolling force F = LwYavg = 30×200×140 = 8.4×105 N = 840 kN
Therefore, the roll force required is 840 kN.
1. Material Science and Engineering
1
Material science – study materials + create new materials
Materials engineering – use materials + create new processes
How are Carbon Fiber Bikes Made
The success of many manufactured products depends on the selection of materials
whose properties meet the requirements of the application.
2. Part 1: Properties – Type of Materials
Metals
Non metals
Metals
Ceramics
Polymers
Composites
• wood, brick, concrete, glass, rubber and
plastics
• weaker, less ductile, less dense, poor
electrical and thermal properties
• metals and its alloys
• luster, high thermal conductivity, and high electrical
conductivity, ductile
Cost of material
Cost of fabricating
Product lifetime
Environmental
impact
Energy
requirements
Recyclability
Advanced Ceramics
Engineered plastics
Hybrid Composites
3. • Properties adequate for the anticipated operating conditions
- mechanical characteristics (strength, rigidity, resistance to fracture, the ability to
withstand vibrations or impacts)
- physical characteristics (weight, electrical properties, appearance)
- features relating to the service environment (ability to operate under extremes of
temperature or resist corrosion) of possibilities
• Taking advantage of the properties
To help evaluate the properties of engineering materials, a variety of standard tests have
been developed .
3
Part 1: Properties (cont’)
4. 4
Physical Mechanical
Density Stress and strain
- strength
- stiffness/modulus
= stress over strain
Melting point
Optical characteristics (transparency,
opaqueness, color)
Thermal properties (specific heat,
thermal expansion, thermal
conductivity, electrical conductivity,
magnetic properties)
Stress/strain?
When a force or load is applied
to a material, it deforms or
distorts (becomes strained),
and internal reactive forces
(stresses) are transmitted
through the solid
Part 1: Properties (cont’)
5. 5
•value displayed on their instrument is a constant
•conducted at the component level in incremental steps to determine structural
integrity
• mechanical loading of a material specimen or product up to a pre-determined deformation level or up to the
point where the sample fails
• further used to characterize the materials and product
Tensile
Compression
Flexural
Impact
Toughness
Part 1: Properties - Testing
7. 7
Process Details Advantage Disadvantage Types
Casting/molding/
foundry
(plastics/composites)
Use molten metal to fill cavity
Metal retains the desired shape of the mold cavity
after solidification
materials can be
converted from a
crude form into a
desired shape in a
single step
excess or scrap
material can easily
be recycled
Need follow-up
process like
machining
1. permanent mold
(a mold can be used
repeatedly)
2. nonpermanent mold
Forming/metal
working/shearing
(metal/plastics that’s
has been previously
casted or moulded)
Basic purpose: modify the shape and size and/or
physical properties of the material
Reference to the temperature of the material at
the time it is being processed with respect to the
temperature at which this material can recrystallize
(i.e., grow new grain structure)
Metal
cutting/machining/ma
terial removal
Removal of certain selected areas from a part in
order to obtain a desired shape or finish,
producing chips
Cutting tools are mounted on in machine tools
which provide the required movements of the tool
with respect to the work (or vice versa) to
accomplish the process desired
machine tools are called
shapers (and planers),
drill presses, lathes, boring
machines, milling machines,
saws, broaches, and grinders
8. 8
Joining and
assembly
The biggest; which includes:
1. Mechanical fastening 4. Press, shrink,
or snap fittings
2. Soldering and brazing 5. Adhesive
bonding
3. Welding 6. Assembly
processes
Surface
treatment/finishing
cleaning, removing residue left by machining, or
providing protective and/or decorative surfaces on
workpieces
include chemical and
mechanical cleaning,
deburring, painting, plating,
buffing, galvanizing, and
anodizing
Rapid prototyping/
additive
manufacturing
(nonmetallic,
metallic,
composites)
fabrication of a physical part, model or assembly
using 3D computer aided design
Prototype components is produced first directly
from the software using specialized machines driven
by computer-aided design packages. The prototypes
can be field tested and modifications to the design
quickly implemented
ability to produce
components with
great precision
and accuracy
Heat treatment heating and cooling of a metal for the specific
purpose of altering its metallurgical and mechanical
properties
Have to know how a selected metal can be altered
by heat treatment, how a selected metal will react
to any heating or cooling that may be incidental to
the manufacturing processes
10. Metal Forming
• Metal forming includes a large group of manufacturing processes in which plastic
deformation is used to change the shape of metal workpieces
• Deformation results from the use of a tool, usually called a die in metal forming,
which applies stresses that exceed the yield strength of the metal
• The metal therefore deforms to take shape determined by the geometry of the die
10
No need to handle molten material or
deal with the complexities of
solidification
Material is simply moved (or
rearranged) to produce the shape,
amount of waste can be substantially
reduced since there are no cutting
away of unwanted region
Forces required are often high
Machinery and
tooling can be quite expensive
Large production quantities may
be necessary to
justify the approach
11. Metal Forming
11
• severe deformation and massive shape
changes
• mostly done in hot working condition
• compressive deformation force
• starting work shapes include billets and
rectangular bars
• small surface area-to-volume
Bulk Deformation
• forming and cutting operations
• performed on thin sheets (<6mm), thin strips
or coils
• mostly done in cold working condition
• tools include punch and die on machine tools
called stamping presses
• high surface area-to-volume
• cross section does not change, only shape
changes
Sheet-metal working/deformation
12. Metal Forming – Hot or cold
is the temperature that a metal begins to
transform from a solid phase into a liquid phase
at the melting temperature, the solid phase
and liquid phase of a metal exist in equilibrium
once this temperature is achieved, heat can be
continuously added to the metal, however this
will not raise the overall temperature.
once the metal is completely in the liquid
phase, additional heat will again continue to
raise the temperature of the metal
12
TA is ambient temperature, Tm is the work metal melting temperature
13. Hot Working Processes
• Involves deformation of preheated material at temperatures above the recrystallization
temperature
• At elevated temperatures, metals weaken and become more ductile
• With continual recrystallization, massive deformation takes place without exhausting
materials plasticity
• Hot working processes includes rolling, forging, extrusion, drawing
13
recrystallization - a process by which deformed grains are
replaced by a new set of nondeformed grains that nucleate
and grow until the original grains have been entirely
consumed
recrystallisation temperature for steels is typically between
400 and 700 °C. The recrystallisation conditions, such as
heating rate and soaking time depend on the degree of cold
work and the steel composition
14. Part 1: Rolling
14
Flow chart for the production of various finished and semifinished steel shapes.
Note the rolling operations.
15. Rolling – Basic Rolling Process
15
• metal is passed between two rolls that rotate in
opposite directions
• because the rolls rotate with a surface velocity that
exceeds the speed of the incoming metal, friction along
the contact interface acts to propel the metal forward
• metal is then squeezed and elongates to compensate
for the decrease in thickness or cross-sectional area
• amount of deformation that can be achieved in a single
pass between a given pair of rolls depends on the
friction conditions along the interface
• If too much is demanded, the rolls cannot advance the
material and simply skid over its surface
• too little deformation is taken, the operation will be
successful, but the additional passes required to
produce a given part will increase the cost of production
17. 17
Hot Rolling
• Temperature is keep at above recrystallization
temperature. For plain-carbon and low-alloy steels, the
soaking temperature is usually about 2200 F (1200 C)
• During the rolling there will be change in its grain
structure, the temperature at recrystallization
temperature will prevent from work hardening
• Due to squeezing action, the grains are elongated in
direction of rolling and velocity of material at exit is
higher than at entry
Hot Rolling
Cold Rolling
• Metal is fed into rolls at below recrystallization
temperature
• To provide smooth and bright finish
• To bring it to accurate size
• To obtain clean surface
Hot rolled metal
cleaned
18. 18
Hot Rolling Cold Rolling
1. Metal is fed into rolls after being heated
above recrystallization temperature
2. Coefficient of friction between rolls and
metal is higher
3. Heavy reduction in cross sectional area is
possible
4. Close dimensional tolerance cannot be
obtained
5. Poor surface finish
6. Does not show work hardening effect
1. Metal is fed into rolls after being heated
above recrystallization temperature
2. Coefficient of friction between rolls and
metal is higher
3. Heavy reduction in cross sectional area is
possible
4. Section dimension can be obtain at close
tolerance
5. Smooth and oxide-free surface
6. Shows hardening effect
20. Advantage of hot rolling
1. greatly reduce energy consumption and costs
- metal plastic deformation is high during hot rolling, and the deformation
resistance is low, which reduces the energy consumption of metal deformation
2. improve the processing performance of metals and alloys
- coarse grains during foundry are broken, the cracks are healed, the casting
defects are reduced or eliminated, and the as-cast microstructure is transformed
into a deformed structure to improve the processing properties of the alloy
3. Hot rolling usually uses large ingots and large reduction rolling, which not only
improves production efficiency, but also creates conditions for increasing rolling
speed and achieving continuous and automated rolling process
20
21. Limitation of hot rolling
1. Delamination
- due to non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the
steel are pressed into thin sheets
delamination greatly deteriorates the tensile properties of the steel in the thickness
direction
2. Residual stress caused by uneven cooling
- residual stress is the internal self-phase equilibrium stress that occurs due to uneven
cooling which can easily happen
3. Uncontrollable mechanical properties
- difficult to control properties required for the product accurately, and the microstructure
and properties of the hot-rolled product are not uniform. The strength index is lower than
that of the cold work hardened product
4. The thickness of the hot rolled product is difficult to control and the control precision is
relatively poor 21
22. Rolling (cont…)
22
Shape rolling
The work is deformed by a gradual reduction into a contoured cross section (I-beams, L-
beams, U-channels, rails, round, square bars and rods, etc.).
Thread rolling
Threads are formed on cylindrical parts by rolling them between two thread dies.
Ring rolling
Thick-walled ring of small diameter is rolled into a thin-walled ring of larger diameter.
24. Rolling (cont…)
24
Defects in Rolled Plates and Sheets
1. Wavy edges on sheets – due to roll bending. The strip is
thinner along its edges than its center.
2. Cracks – poor material ductility at the rolling temperature
3. Alligatoring – due to non-uniform deformation during rolling or
defects in the original cast billet.
26. Rolling (cont…)
26
The work is squeezed between two rolls so that it
thickness is reduced by an amount called the draft, d
d = to-tf
If the draft is expressed as a fraction of the starting block
thickness, it is called reduction, r:
r = d/to
Rolling increases the work width from an initial value of wo
to a final one of wf, and this is called spreading.
27. Rolling (cont…)
27
The inlet and outlet volume rates of material flow must be the same,
that is,
towovo = tfwfvf
where vo and vf are the entering and exiting velocities of the work.
The power P required to drive each roll is :
P=2πNFL
where N is the rotational speed of the roll, F is the rolling force and L
is the roll strip contact length.
L2 = Rd, R is the roll radius.
F = LwYf, Yf is the average stress, w strip width.
28. Example
An annealed copper strip, 200mm width and 25mm thick is
rolled to a thickness of 20mm in one pass. The roll radius is
300mm and the rolls rotate at 100rpm. Calculate the roll
Force required in this operation. Yavg is 140 Mpa.
28
