Group 8 – Chapters 13 and 14
•Jason Becker
•Andrew Nawrocki
•Ryan Niehaus
•Jonathan Ogaldez
•Stephen Wakeland
Chapter 13
•Rolling of Metals
Introduction
• Movie
Introduction
• Rolling
– The process of reducing the thickness or
changing the cross-section of a long
workpiece by compressive forces applied
through a set of rolls
– Not just for metal
• Used to enhance plastics, powder metals,
ceramic slurry, and hot glass
Introduction
Introduction
• First step
– Generally an ingot or continuous cast
metal is "hot" rolled at elevated
temperatures
• Enhances material hardness and strength
• "Cold" rolling
– The material can be rolled at room
temperature
• Enhances strength, hardness, and surface finish
• Requires more energy
Introduction
• Plates
– Thickness of >6mm
• Structural applications
– Ship hulls, boilers, bridges, machinery, and nuclear
vessels
• Sheets
– Thickness of <6mm
• Typically provided as coils or flat sheets
• Large variety of applications
Flat-Rolling Process
• Roll gap, L
– Where reduction occurs
• Relative sliding
– To the right of the no-slip point, material
moves faster than the roll
– To the left of the no-slip point, material
moves slower than the roll
Flat-Rolling Process
• Draft
– Difference between the initial and final
strip thicknesses (ho – hf)
• Frictional Forces
– Required to move workpiece
– Must be overcome, increasing rolling
forces and power requirements
Flat-Rolling Process
• Roll force
– Lateral force required to compress the
workpiece
– Perpendicular to the plane of the strip
Flat-Rolling Process
• Reducing roll force
– Reducing friction
– Using smaller-diameter rolls
– Taking smaller reductions-per-pass
– Rolling at elevated temperatures
– Applying tensions to the strip
Flat-Rolling Process
• Tension (Longitudinal Force)
– Back tension
• Force applied to the strip at the entry zone
• Apply a braking action to the reel supplying the
sheet into the roll gap (pay-off reel)
– Front tension
• Force applied to the strip at the exit zone
• Applied by increasing the rotational speed of
the reel receiving the sheet from the roll gap
(take-up reel)
Flat-Rolling Process
• Geometric considerations
– Due to roll forces, rolls may bend
(deflection)
• Causes the rolled strip to be thicker at its
center than at its edges (crown)
• Corrected for by making the rolls larger
diameter at their center (camber)
• To counteract deflection, the rolls can also be
externally bent at their bearings
Flat-Rolling Process
Flat-Rolling Process
• Spreading
– Strips with a more square cross-section
will cause its width to increase
significantly during rolling
– Increases with:
• A decrease of width-to-thickness ratio
• Increase of friction
• Decrease of ratio of the roll radius to the strip
thickness
Flat-Rolling Process
• Vibration and chatter
– Have significant effects on product quality
and productivity of metalworking
operations
– Chatter
• Self-excited vibration
• Can occur in rolling, extrusion, drawing,
machining and grinding
• Leads to periodic variations in the thickness of
the sheet and its surface finish
• Rolling speed and lubrication are the two most
important parameters
Flat-Rolling Practice
• Initial Hot Rolling
– Cast structure includes coarse and nonuniform grains
– Hot rolling converts this to a wrought
structure with finer grains and enhanced
ductility
Flat-Rolling Practice
Flat-Rolling Practice
• First hot-rolling product
– Slab
• Large rectangular cross-section
– Bloom
• Large square cross-section
– Billet
• Square cross-section smaller than a bloom
Flat-Rolling Practice
Flat-Rolling Practice
• Conditioning
– Surface of the slab, bloom, or billet must
be prepared for subsequent rolling
• Torch (scarfing) to remove heavy scale
• Rough grinding to smoothen surfaces
– Prior to cold rolling
• "Pickling" with acid (acid etching)
• Blasting with water
• Grinding
Flat-Rolling Practice
• Cold rolling
– Carried out at room temperature
– Produces sheets and strips with:
• Better surface finishes (lack of scale)
• Better dimensional tolerances
• Better mechanical properties
• Pack rolling
– Two or more layers of metal are rolled
together to improve productivity
– Aluminum Foil
Flat-Rolling Practice
• Defects
– Adversely affect strength, formability, and
other manufacturing characteristics
– Wavy edges (a)
• Result from roll bending and is thinner along its
edges than at its center
– Cracks (b & c)
• Usually result from poor material ductility
– Alligatoring (d)
• Typically caused by defects in the original cast
material
Flat-Rolling Practice
Flat-Rolling Practice
• Other characteristics
– Residual stresses
• Small-diameter rolls tend to deform the metal
more at its surface than in its bulk
• Large-diameter rolls tend to deform the metal
more in its bulk than at its surface
Flat-Rolling Practice
• Other characteristics (cont'd)
– Dimensional tolerances
• Thickness tolerances for cold-rolled sheets are
more stringent than for hot-rolled sheets
• Due to thermal effects, the final thickness of
hot-rolled sheets is more difficult to predict
– Surface roughness
• Hot-rolled sheets are likely to require finishing
operations, while cold-rolled sheets likely are
not
– Gage numbers
• Smaller number = thicker sheet
Section 13.4 Rolling Mills
Hot Rolling
Cold Rolling
Types of Mills
Materials
Lubricants
Types of Mills
• Two-High
Rolling Mills
• Three-High
Rolling Mills
• Four High
Rolling Mills
• Cluster Mills
• Tandem
Rolling
Two-High Mills
• Used for hot
rolling in the
initial passes
• Used on cast
ingots
• Used in
continuous
casting
• Roll diameters
.06m-1.4m
Three-High Mills
• Aka reversing
mills
• Plate or
material being
rolled will be
raised and
lowered
throughout
the machine
from upper to
lower roll
gaps.
Four-High Mills
• Same principles as cluster mills,
Sendzimir mills or Z mills
• Utilize smaller rolls for lower roll
forces
• Also lower power requirements
and reduce spreading
• Rolls are cheaper to replace
• Small rolls deflect more so they
must be supported by smaller
rolls
• Very adept for cold rolling thin
sheets high-strength materials
Four-High Rolling Mill
Cluster, Sendzimir or Z mill
Tandem Rolling
• Strip of Material
continuously rolled through
several stands
• Gauges of stands get
smaller progressively
• Each stand (train) has its
own rolls
• Requires highly automated
systems to control thickness
and speed
Tandem Rolling Mill
Rolls
• Rolls must be made of materials with
high strength and resistance to wear
• Common materials include cast iron,
cast steel and forged steel
• Forged steel has higher strength,
stiffness and toughness but costs
more
• Tungsten carbides can be used for
smaller diameter rolls
• Rolls are polished for cold-working
and special applications
• Rolls are heat specific-misuse results
in heat checking and spalling
Lubricants
• Hot Rolling Ferrous alloysNone or Graphite
• Hot Rolling Non-Ferrous
Alloys-Oils, emulsions and
fatty acids
• Cold Rolling-Oils, emulsions,
paraffin and fatty oils
13.5 Various Rolling Processes and Mills
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•
•
•
•
•
•
Shape Rolling
Roll Forging
Skew Rolling
Ring Rolling
Thread rolling
Rotary Tube Piercing
Tube Rolling
Shape Rolling
• Used for straight and long
structural shapes
• I-beams, rails, channels
• Structures usually formed at
higher temperatures
• Requires a series of rolls
(material deformed nonuniformly)
Shape Rolling
Roll Forging
• Aka cross rolling
• Cross section of a
round bar is
shaped by passing
it through rolls
with varied groves
• Used to produce
leaf springs,
knives and hand
tools
Skew Rolling
• Similar to roll
forging
• Used for making
ball bearings
• Wire/rod is fed
into the roll gap
to form spherical
blanks
Ring Rolling
•
•
•
•
•
•
Used to create large rings for rockets
and turbines, jet engine cases,
flanges and reinforcing rings for
pipes
Involves using two rollers to expand
a thick small ring into a thin large
ring
Utilizes a series of rollers, driven and
stationary
The rings thickness is reduce while
its diameter is increased (volume of
material stays the same.
Pieces can be as big as 3m in
diameter
Advantages: short production time,
close tolerances, material savings,
increased strength (favorable grain
flow)
Thread Rolling
• Thread s are formed on round rods or wire by
passing between dies
• Cold forming process
• Two reciprocating dies or rotary dies
• Used to create threads on screws, bolts etc.
• Production rates of up to 80 pieces per second
• Generates treads with good strength (cold
working)
• Compressive residual stresses improve fatigue
life
• Gears can also be produce in a similar manner
• Lubrication is especially important in thread
rolling for finish surface and integrity
Rotary Tube Piercing
• Aka Mannesmann
Process
• Used to make long,
thick-walled
seamless pipe and
tubing
• Hot working
process
• Developed in the
1880’s
• Rolled bar under
cyclical compression
develops a cavity
that grows down
the tube
• Cavity is then
expanded/pierced
by a floating
mandrel
Tube Rolling
• Process used
to reduce the
diameter and
thickness of
pipes/tubes
• With or
without
mandrels
• Process can
be stepped
13.5.1
Integration Mills
Large facilities
that integrate
the entire
production of a
part
Includes:
production of
metals, casting
rolling and the
finished product
MiniMills
Recycles scrap
metals, usually from
local sources to
reduce cost, and
casts and rolls the
metals
Usually only produce
one kind of product
(rod, bar, angle
iron)
Forging of metals
– Forging is the basic process which the
material is shaped by compressive
forces that is applied through various
tools and dies.
– Forging operations create discrete parts
– Forged parts have good strength and
toughness because the grain of the
metal can be controlled, thus making
ideal for highly stressed applications,
such as large rotors for turbines, gears,
bolts and rivets, railroads, aircraft, and a
variety of other transportation
equipment.
Open-Die forging
– Simplest type of forging
– Dies are inexpensive
– Wide range of part
sizes, ranging from 301000lbs
– Good strength qualities
– Generally good for small
quantities
– Limited to simple shapes
– Difficult to hold close
tolerances
– Needs to be machined
to final shape
– Low production rate
– Poor utilization of
materials
– Highly skilled operation
1100 Ton Hydraulic
Forging Press
and 20 Ton Capacity
Manipulator
Open-Die forging
Impression Die Forging
– Better properties of
Open Die Forgings
– Dies can be made of
several pieces and
inserts to create more
advanced parts
– Presses can go up to
50,000 ton capacities
– Good dimensional
accuracy
– High production rates
– Good reproducibility
– High die cost
– Machining is often
necessary
– Economical for large
quantities, but not for
small quantities
Completed part
before removal of
the flash
Impression Die Forging operation
– This form of forging
is used to make more
complicated parts
from Blank bar stock.
The Blanks are
compressed between
two or more dies to
shape the part. Once
the part is shaped,
the flash is removed
by either grinding it,
trimming, or
machining.
Precision Forging
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–
–
–
–
–
–
Close dimensional tolerances
Very thin webs and flanges are
possible
Very little or no machining is required
Little or no scrap after part is
produced
Cheaper to produce from less finishing
operations and faster production
Typical applications are gears,
connecting rods, and turbine blades
Common materials used in precision
forging are aluminum, magnesium
alloys, steel, and titanium
Some examples of precision forged
products: Piston heads, connecting
rods, and turbocharger fans
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–
–
–
–
High forging forces
Thus higher capacity equipment is
required
Intricate dies leading to increased
die cost
Precise control over the Blank’s
volume and shape
Accurate positioning of the Blank
in the die cavity
Forging Operations
•
•
•
•
•
Coining
Heading
Piercing
Isothermal forging
Rotary and tube swaging
Coining
• Closed die system
• Can produce fine detail
• Lubrication cannot be used
Heading
• Also called upset forging
• Care must be taken so that work
piece does not buckle
• Can be highly automated
Piercing
• Used to make indentations on the surface of
the work piece
• Force depends on the cross-sectional area of
the punch
Isothermal Forging
• Also known as hot die forging
• Complex parts with good dimensional accuracy
can be made
• It is expensive and has low production rates
• Can be economical for intricate forge designs.
• Aluminum, titanium, and other super alloys are
typically used
Rotary Swaging
• Rotary swaging
– Work piece remains stationary
while the dies rotate
– Dies strike the piece up to 20
times a second
– Dimensional tolerances are around
.05 to .5m
– Suitable for medium to high
production rates
Tube swaging
• Used to decrease the diameter of a
tube with or without a mandrel
Forgeability of Metals
- Upsetting test
• Uses 2 flat dies
Hot twist test
– The specimen is twisted until
failure
– Done at different
temperatures
– The temperature related to
the maximum twists becomes
the forging temperature.
Forging Defects
• Insufficient material causes laps (voids in the work piece)
• Excessive material causes internal cracks
Grain-flow pattern
• If the pattern is perpendicular to the
surface, which is called end grains,
the environment can attack the
surface making it rough.
Die Design, Materials, and Lubrication
• Die design relies on the properties of the work piece,
distortion, most importantly the knowledge of the material
flowing to the least resistance.
• Software has helped model the forging process
• Design features
– The parting line is at the largest cross-sectional area
– Designed in such a way that the dies lock together
– Flash is limited to 3% of the greatest thickness of the
part
– Draft angles are necessary in almost all forging
• Internal angles range from 7 to 10 degrees
• External angles range from 3 to 5 degrees
– Careful selection of radii for corners and fillets
• Small radii tend to wear the die and shorten it’s life
Die Materials and Lubrication
• General requirements
– Strength and toughness at high
temperatures
– Hardenability
– Resistance to thermal and
mechanical shock
– Wear resistance
• Lubrication
– Reduce friction and wear
– Act as a thermal barrier
– Act as a parting agent
14.7, 14.8, 14.9
DIE FAILURES,
FORGING MACHINES,
AND ECONOMICS OF FORGING.
14.7 DIE MANUFACTURING METHODS- DIE
FAILURES
• DIES, MANUFACTURING
METHODS.
• DIE COSTS
• DIE FAILURES
MANUFACTURING METHODS
• CASTING- object formed by a mold
• FORGING- forming a hot or cold metal into a
fixed shape by hammering, pressing or rolling
• MACHINING- To remove excess or unwanted
stock by use of machine tools for rough or
finish turning, boring, drilling or milling
• GRINDING- to reduce the amount of material
by pressure or impact
• ELECTRICAL AND ELECTRO-CHEMICAL
METHODS (EDM)- uses an electrode to create
a hole or cut.
• LASERS- An intense light beam used to create
a cut and shape material
DIE COSTS
• GREATLY DEPENDS ON THE
SIZE
• SHAPE AND COMPLEXITY
• APPLICATION
• SURFACE FINISH
• DIE MATERIAL AND
MANUFACTURING
DIE FAILURES
• Improper design
• Defective heat-treatment
finishing operations
• Overheating and heat checking
(causes cracking)
• Excessive wear
• Overloading
• Improper alignment
• Misuse of die
• Improper handling
14.8 FORGING MACHINES
•
•
•
•
•
•
•
HYDRAULIC PRESSES
MECHANICAL PRESSES
SCREW PRESSES
HAMMERS
DROP HAMMERS
COUNTERBLOW HAMMERS
HIGH-ENERGY-RATE FORGING
(HERF) MACHINES
Hydraulic and Mechanical press
• Hydraulic Press- are slower and involve higher
initial costs, and require less maintenance. They
consist of a frame with two or four columns,
pistons, cylinders, rams, and hydraulic pumps
driven by electric motors.
• Mechanical Press- are crank or centric type,
they are stroke limited the energy is generated by
a large flywheel power by an electric motor.
Left a mechanical press
Right a hydraulic press
Principles of Various Forging
Machines (cont.)
Figure 14.21 (continued) Schematic illustration of the principles of various forging
machines. (c) Knuckle-joint press. (d) Screw press. (e) Gravity drop hammer.
Screw Presses
• Screw presses- derive their energy from a flywheel
and are energy limited. The forging load is
transmitted by a large vertical screw, and ram
comes to a stop when energy is used up. They are
used for open-die and closed-die forging
operations. Used for small production quantities
and for thin parts.
Hammers, drop hammers and
counterblow hammers.
• Hammers- derive their energy from the potential
energy, which is then converted into kinetic
energy, which makes them energy limited. To
complete forging several successive blows are
usually made onto the same die. They are the
most versatile and least expensive type of
forging equipment.
• Drop hammers- the ram is accelerated by a
steam air or hydraulic pressure usually 750kPa.
• Couterblow hammers- This type has two rams
that simultaneously approach each other
horizontally or vertically to forge a part. They
operate in high speeds and transmit less
vibrations to their base.
High-energy-rate forging (HERF)
machines.
• HERF machines- in this type of machine
the ram is accelerated rapidly, by high
pressures and gases, and parts are forged
usually with one blow at very high speeds.
• Problems with HERFS machines- there are
problem with maintaining such machines
and operating them are also a hassle.
Safety and die breakage are considerations
that cause problems with HERFS and make
them undesirable to the industry.
14.9 Economics of Forging
•
•
•
•
Complexity of the forging
Tool and die costs
Die material
Size of forgings
Works Cited
• http://www.me.gatech.edu/jonathan.colton/me4210/deform.h
tml
• http://images.google.com/imgres?imgurl=http://wwwmaterials.eng.cam.ac.uk/mpsite/process_encyc/pictures_for_d
etails/forging4.jpg&imgrefurl=http://wwwmaterials.eng.cam.ac.uk/mpsite/process_encyc/nonIE/forging.html&h=264&w=330&sz=22&tbnid=RzDAS5ziYax5
NM:&tbnh=91&tbnw=114&hl=en&start=13&prev=/images%3
Fq%3Dforging%2Bflash%26svnum%3D10%26hl%3Den%26l
r%3D%26safe%3Doff
• http://www.qcforge.com/rapidIR/
• http://cmpmedia.globalspec.com/AluminumPrecisionProducts?
VID=138521&deframe=1
• http://images.google.com/imgres?imgurl=http://www.fushen
g.com/precision/images/casting.jpg&imgrefurl=http://www.fu
sheng.com/precision/&h=252&w=320&sz=30&tbnid=rEG6iitN
YwFdhM:&tbnh=88&tbnw=113&hl=en&start=69&prev=/imag
es%3Fq%3Dprecision%2Bforging%26start%3D60%26dnum
%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26safe%
3Doff%26sa%3DN
Works Cited
• step.polymtl.ca/~coyote/ dragonlance_misc.html
FORGING OLD MAN AND MIGET
• www.airhydraulics.com/. ../Animation.htm
Hydraulic press.
• Kalpakjian Schmid Manufacturing Engineering and
Technology copy 2001 Prentice-Hall page 347-395
• www.qform3d.com/ en/62.html animation for
mechanical press
• www.farthingales.on.ca/ bone_tip_machines.html
press and dies steel “real”
• www.emeraldsurgical.com/ production_tour.htm
forging pic with red glow
Works Cited
• http://www.msm.cam.ac.uk/phasetrans/2002/FR.html