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Manufacturing Fundamentals

The document discusses the rolling process, a deformation method that reduces the thickness of materials through compressive forces from opposing rolls, primarily in hot working. It outlines the definitions of various rolled shapes (bloom, slab, billet), advantages and disadvantages of rolling, and details the mechanics and calculations involved in flat rolling, including draft, spreading, and rolling force. Additionally, it touches on rolling defects and introduces the deep drawing process, a sheet metal forming operation, along with its mechanics and potential defects.

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salmaeyomi
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5 views26 pages

Manufacturing Fundamentals

The document discusses the rolling process, a deformation method that reduces the thickness of materials through compressive forces from opposing rolls, primarily in hot working. It outlines the definitions of various rolled shapes (bloom, slab, billet), advantages and disadvantages of rolling, and details the mechanics and calculations involved in flat rolling, including draft, spreading, and rolling force. Additionally, it touches on rolling defects and introduces the deep drawing process, a sheet metal forming operation, along with its mechanics and potential defects.

Uploaded by

salmaeyomi
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Rolling Process

Rolling is a deformation process in


which the thickness of work is reduced
by compressive forces exerted by two
opposing rolls. Most rolling is carried
out by hot working called hot rolling.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 1


Rolling
• One of the first primary
processes to convert raw
material into a finished
product.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 2


Definitions
The ingot is rolled into 3 shapes:
 Bloom:
A bloom has a square cross-section 150mm x
150mm or larger.
 Slab:
A slab is rolled from an ingot or a bloom and has
a rectangular cross-section of width 250mm or
more and thickness 40mm or more.
 Billet:
It is rolled from a bloom and is square with
dimensions 40mm x 40mm or more

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Steel Products made by Rolling

01/11/2024 Prof. Dr. Salah A. Elsheikhi 4


Advantages and Disadvantages of Rolling

1. Advantages
 Large amount of deformation,
 No residual stresses,
 Isotropic properties.
Disadvantages
 Can not be held to close tolerances,
 Oxide scales on the surface.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 5


Analysis of Flat Rolling
 It is the rolling process in which the work is
squeezed between two rolls to reduce the
thickness by an amount called the draft.

Draft is the reduction of thickness in flat rolling by


squeezing it between 2 rolls.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 6


Analysis of Flat Rolling (cont.)
Draft, d
d = to – tf
 d- draft, mm
 to – starting thickness,mm

 tf – final thickness, mm
Reduction, r
r = d/to
r= 1 - tf/to

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Spreading
 Spreading is the increase in work width during
rolling.
 According to volume constancy:
to wo L o = t f wf L f
 According to flow rate constancy:
t o w o v o = tf w f v f

01/11/2024 Prof. Dr. Salah A. Elsheikhi 8


Spreading of a
Strip in Flat
Rolling

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Description of the Rolling Process
 The rolls contact the work along a contact
arc angle Ө.
 Surface velocity of roll (vr) > Entering speed
of the work (vo).
 Surface velocity of roll (vr) < Exit speed of
the work (vf).
 There is a gradual change in the work speed
between the rolls.
 There is a point in which the roll velocity
equal to work velocity, this point is called
Neutral point or no-slip point.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 10


01/11/2024 Prof. Dr. Salah A. Elsheikhi 11
Forward Slip, S
 It is the slip between roll and work.
S = (vf – vr )/vr
 S – forward slip,
 vf – final velocity of the work, m/s

 vr – roll speed, m/s

01/11/2024 Prof. Dr. Salah A. Elsheikhi 12


True Strain & Average flow stress
Є= ln to/tf

Yf = KЄn / n+1
Maximum draft in case of friction
dmax = μ2R

dmax - Maximum draft, mm


μ – Coefficient of friction
R – Roll radius, mm

01/11/2024 Prof. Dr. Salah A. Elsheikhi 13


Calculation of the Rolling Force

 Rolling Force = Average flow stress x Area


F = Yf W L
Contact Length, L:

L  Rto  t f 

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Torque is the moment in the middle of the contact length

The power required for rolling, P=Tω


ω for one roll=2ΠN, for 2 rolls ω=4 ΠN

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01/11/2024 Prof. Dr. Salah A. Elsheikhi 16
Rolling Defects
 Waviness
 Improper roller

speeds
 Zipper cracks
 Too much rolling in

center
 Edge cracks
 Too much rolling

on outside
 Alligatoring
 Too much induced

tensile stress in the


part.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 17


DEEP DRAWING PROCESS

01/11/2024 Prof. Dr. Salah A. Elsheikhi 18


WHAT IS DEEP DRAWING?
 It is a sheet metal
forming operation to
make cup-shaped,
box-shaped, or other
complex-curved,
hollow-shaped parts.
 It is performed by
placing a piece of
sheet metal over a
die cavity and then
pushing to metal into
the opening with a
punch.
01/11/2024 Prof. Dr. Salah A. Elsheikhi 19
01/11/2024 Prof. Dr. Salah A. Elsheikhi 20
01/11/2024 Prof. Dr. Salah A. Elsheikhi 21
STAGES IN DEFORMATION DURING DEEP DRAWING

Bending Straightening
Initial contact between
punch and work

Friction &
compression Final cup
shape

01/11/2024 Prof. Dr. Salah A. Elsheikhi 22


Mechanics of Drawing
Db : blank diameter,
Dp : punch diameter,
Rp : punch corner radius,
Rd : die corner radius.
C : clearance between punch and
die.
C= 1.1t
F : drawing force,
Fh : holding force

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 MEASURES OF DRAWING:

1. Drawing Ratio, [ DR=Db/Dp]

2. Reduction, [ r= (Db – Dp)/ Db]

3. Thickness to diameter ratio, [t/ Db]

01/11/2024 Prof. Dr. Salah A. Elsheikhi 24


DRAWING FORCE
F=π.Dp.t.(TS).(Db/Dp – 0.7)
Where, F is drawing force, t is original blank thickness; TS is tensile strength; and Db and Dp
are the starting blank diameter and punch diameter, respectively. The constant 0.7 is a
correction factor to account for friction

HOLDING FORCE
Fh=0.015 Yπ[Db2 – (Dp+2.2t + 2Rd)2]
Where, Fh is holding force in drawing; Y is yield strength of the sheet metal; t is
starting stock thickness; Rd is die corner radius; and the other terms have been
previously defined.

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DEFECTS OF DEEP DRAWING
A number of defects in drawing can occur, which include:

(a) Wrinkling in the flange occurs due to compressive buckling because of a small
blank holder force.
(b) Wrinkling in the wall takes place when a wrinkled flange is drawn into the cup.
(c) Tearing occurs because of high tensile stresses that cause thinning and failure of
the metal in the cup wall. Tearing can also occur in a drawing process if the die
has a sharp corner radius.
(d) Earring occurs when the material is anisotropic, i.e. has varying properties in
different directions.
(e) Surface scratches can be seen on the drawn part if the punch and die are not
smooth or if the lubrication of the process is poor.

01/11/2024 Prof. Dr. Salah A. Elsheikhi 26

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