MECH2305
Introduction to Engineering Design and Manufacturing
Metal Forming (Part II)
Rolling
Dr Dan Yuan
School of Mechanical & Mining Engineering, UQ, EAIT
d.yuan@uq.edu.au
Metal Forming Lecture Series
Part I
❑ Theory of Deformation Processing
❑ Forging
Part II
❑ Rolling
❑ Extrusion and Drawing
Reference: Kalpakjian: Chapter 13, 14, 15
Outline of Lecture
• Introduction to Rolling
• Types of Rolling Mill
• Rolling Defects
• Rolling Load Calculations
Reference: Kalpakjian: Chapter 13
What is Rolling?
“Process of reducing the
thickness or changing the cross
sectional shape of a long
compressive
workpiece by _____________
forces applied through a set of
rolls”
Rolling changes the • Breaks down coarse grains to
finer grains
microstructure of • Closes up porous structures
metals • Improves mechanical properties
Introduction to Rolling (Video)
2:45
https://www.youtube.com/watch?v=KRn73gKQ2YU
Rolling
Rolling can be done at elevated temperature or room
temperature
Two basic types of rolling:
1. Flat rolling
2. Shape rolling
Using two-high rolling Rolling
in cogging mill
• Hot rolling: Initial ingot
breakdown to blooms,
billets & slabs
Rolling
• Hot rolling to plate
(thickness > 6mm), sheet
(< 6mm), bar, pipe, rails,
structural shapes
Steels start at 1000-1300°C
Finish 700-900°C
Rolling
• Cold rolling to sheet
strip & foil
(Al foil < 3 ~ 8 m)
• Superior tolerances
& surface finish
(stainless steels to
mirror quality)
• Higher strengths
with cold work
Rolling Mill
Rolling mill consists of:
• Rolls (shaping)
• Bearings (to allow rotation)
• Housing (to keep rolls
together)
• Drive (to apply power and
control speed)
Flat Rolling
Two high rolling • Two high rolling mill
• Simplest; rolls of equal size
• rolls spin in opposite direction
• Large rolls with large reductions
used for initial ingot at high
temperatures
• Draft, h = ho - hf
Flat Rolling : Types of Rolling Mills
Two-high Three-high
Two-high mill
Reversing mill mill
Flat Rolling : Types of Rolling Mills
Four-high Six-high Cluster mill
mill mill (Sendzimir Mill)
Flat Rolling: 4 and 6 High Mills
Four high rolling Six high rolling
• Decrease roll force if work rolls are small
• Bigger rolls adds stiffness (stops deflection)
• Needed for thin sheet & foil
Flat Rolling: Cluster Mill
Cluster rolling or Sendzimir mill
• Developed for producing extremely thin gold foil
Shape Rolling
Products:
H, I-beams, rounds, rails,
hexagonal, channels,
angles, railway, etc.
Metal forming process that involve
forming the work with rolls of a certain
geometry
Case Study: Skew Rolling Process
• Can be used to produce discrete, spherical shapes (e.g.
steel balls)
Tandem Rolling
• Series of mills in
tandem for high
production rates (e.g.
Cu radiator foil from 25
mm to 40 m
thickness)
• Velocity of workpiece
increases at each roll
as thickness decreases
(width is constant)
• Shape or flat rolling
Rolling Defects
(a) Wavy edges: Strip is
thinner along edges
than centre and edges
buckle.
(b,c) Cracks: ductility of
material is too low
(d) Alligatoring: non-uniform
deformation during
rolling
More information: Kalpakjian Section 13.3.1
Roll Design: Roll Material
Uses ferrous alloys
1. Steels (< 2%C)
• Roughing stands
• Adamites, high chromium
iron (HCr), high speed
steels (HSS)
2. Cast Iron (> 2% C)
• Finishing stands
• Chilled cast iron, spheroidal
cast iron, high Cr cast iron
Roll Design: Influence of Roll deflection
• The rolled strip tends to be
thicker at its centre than at
edges (crown)
• To overcome this, grind the
roll larger (~ 0.25 mm) in
diameter at its centre than at
edges (camber)
• Use external moment to
compensate
Calculation of Rolling Forces
𝑭𝒓𝒐𝒍𝒍𝒊𝒏𝒈 = 𝑭𝒍𝒐𝒘 𝑺𝒕𝒓𝒆𝒔𝒔 ∗ 𝑨𝒓𝒆𝒂 𝒐𝒇 𝒄𝒐𝒏𝒕𝒂𝒄𝒕
Area of contact (tool bite area)
= Width * Roll strip contact
length (L)
𝑨 = 𝒘 ∗ 𝑹(𝒉𝟎 − 𝒉𝒇 )
Flow stress = average true stress
derived from true strain
ℎ
Step 1: 𝜀 = ln(ℎ0 )
𝑓
Step 2: use plot to get flow
https://matmatch.com/learn/process/cold-rolling stress depending on metal
Calculation of Rolling Forces
Roll forces (F) and the total power (P) can be calculated using
the following equations:
𝑭𝒓𝒐𝒍𝒍𝒊𝒏𝒈 = 𝑳 ∗ 𝒘 ∗ 𝒀𝒂𝒗𝒈 𝑳 = roll-strip contact length
𝒘 = width of the strip
𝑳= 𝑹(𝒉𝟎 − 𝒉𝒇 )
𝒀𝒂𝒗𝒈 = average true stress
𝑵 = roll speed in rpm
𝑭𝒓𝒐𝒍𝒍𝒊𝒏𝒈 = 𝑹((𝒉𝟎 − 𝒉𝒇 ) ∗ 𝒘 ∗ 𝒀𝒂𝒗𝒈
𝑹 = roll radius
𝒉𝟎 = initial thickness
𝟐𝝅𝑭𝑳𝑵 𝒉𝒇 = final thickness of the strip
𝑷=
𝟔𝟎𝟎𝟎𝟎
Equations for F does not consider
𝒓𝒆𝒗
𝟐𝝅(𝒏𝒆𝒘𝒕𝒐𝒏)(𝒎𝒆𝒕𝒆𝒓𝒔)( ) friction; actual force may be
𝑲𝑾 = 𝒎𝒊𝒏
𝟔𝟎𝟎𝟎𝟎 estimated by increasing F by 20%
Refer to Kalpakjian Section 13.2 for more details and example
Questions: Rolling
1. True or False. The rolling process can only produce a
simple, flattened shape profile. FALSE
2. True or False. The rolling process can only produce
continuous shapes. FALSE
3. This type of rolling process is best for producing very thin
metal foils:
a. three-high mill c. cluster mill
c
b. two-high mill d. six-high mill
4. True or False. As the diameter of the work roll decreases,
the rolling load decreases. TRUE
