2. 2
Introduction
First developed in late 1500’s
Accounts for 90% of all metals produced by
metal working processes
Basically process involves reducing thickness
or changing cross section of long piece by
application of compressive forces through a
set of rollers
Basic process is flat rolling produces flat plate
and sheet
3. 3
Difference between Plates and Sheet
Plates:
Thickness > 6 mm (max. up to 0.3 m)
Used for structural applications e.g. machine
structure, ship hulls, boilers, bridges, nuclear
vessels
Sheets:
Thickness < 6 mm
Used as flat pieces, strips in coil in automobile,
aircraft bodies, appliances, food & Beverages
container, kitchen & office equipments, etc.
4. 4
Typical examples of sheets:
In Boeing 747 skin thickness is 1.8 mm.
In Lockheed L1011 skin thickness is 1.9 mm.
Aluminum beverage cans are 0.1 mm thick.
Aluminum foils used for wrapping candies and
cigarettes is 0.008 mm thick.
5. 5
The process of plastically deforming a metal by passing it
between rolls; a reduction in thickness results from
compressive stresses exerted by the rolls
This is the most widely used metalworking process because
it lends itself to high production and close control of the final
product.
Rolling
6. 6
The principal rolling processes are hot rolling and
cold rolling
Hot rolling is the most common method of refining the
cast structure of ingots and billets to make primary
shapes
Bars of circular or hexagonal cross section like I
beams, channels, and railroad rails are produced in
great quantity by hot rolling with grooved rolls
Cold rolling is most often a secondary forming
process that is used to make bar, sheet, strip, and foil
with superior surface finish and dimensional
tolerances
Hot Rolling & Cold Rolling
7. 7
Flat Rolling
Start with slab like ingot (as large as 30 ft by
2ft by 10 ft)
Pass through two rolls separated by a
distance less than the thickness of the ingot
Keep passing through such rolls until the
final thickness is achieved
If the final material is thin enough (i.e. Less
than 0.25 in) coil it.
9. 9
MECHANICS OF ROLLING
A
N
C
Vo Vf
Vr
t
a
R
L
hf
ho
S
R
Dh/2
D
E
Conservation of volume implies: Vo.ho.w=Vf.hf.w.
Since hf < ho, and w = constant; so Vf > Vo.
10. 10
MECHANICS OF ROLLING(Contd.)
To the left of N, since Vr>Vo, so frictional stress on the
work piece is directed anticlockwise, as shown.
Conversely, to the right of N, we have Vr<Vf, and so
the frictional forces are directed clockwise, as shown.
A
N C
Vo Vf
Vr
t
a
R
L
hf
ho
S
R
Dh/2
D
E
14. 14
TORQUE AND POWER
Tapplied
L/2
F
Free body of Roll
Tapplied=F.L/2, where L=(RDh)1/2
R
Power =T.2pN/60 where N is in rpm,
for single roll per pass.
L
R
S
Dh/2
m.p
F
Free body of
workpiece
ho hf
F= L W YAVG , where L=2a,
w=width, YAVG =True stress
15. 15
EFFECTIVE Y' IN WORK HARDENING
MATERIAL
(Applicable In Forging, Rolling, Extrusion Operations)
When the material has work hardening, then one can use an
average Y that represents the total strain imposed on the
material.
e experienced by
workpiece, e.g., e=ln(ho/hf)
Yav.
1
K
Yav.
or,
x
Yav.
x
Vol.
1
x
.
x
.
x
.
1
0
0
n
n
K
Vol
d
K
Vol
d
σ
Vol
done
Work
n
n
n
e
e
e
e
e
e
e
e
