Metal Forming Process

Unit III
Metal forming process

Three Basic Bulk Deformation
Processes
1. Rolling – slab or plate is squeezed between
opposing rolls
2. Forging – work is squeezed and shaped
between opposing dies
3. Extrusion – work is squeezed through a die
opening, thereby taking the shape of the
opening

Deformation process in which work
thickness is reduced by compressive
forces exerted by two opposing rolls
The rolling process (specifically, flat rolling).
Rolling

The Rolls
Rotating rolls perform two main functions:
 Pull the work into the gap between them by
friction between workpart and rolls
 Simultaneously squeeze the work to reduce its
cross section

Types of Rolling
 Based on workpiece geometry :
 Flat rolling - used to reduce thickness of a
rectangular cross section
 Shape rolling - square cross section is formed into a
shape such as an I-beam
 Based on work temperature :
 Hot Rolling – most common due to the large amount
of deformation required
 Cold rolling – produces finished sheet and plate
stock

Some of the steel products made in a rolling mill.
Rolled Products Made of Steel

Side view of flat rolling, indicating before and after thicknesses, work
velocities, angle of contact with rolls, and other features.
Diagram of Flat Rolling

Rolling Mills
 Equipment is massive and expensive
 Rolling mill configurations:
 Two-high – two opposing rolls
 Three-high – work passes through rolls in both
directions
 Four-high – backing rolls support smaller work rolls
 Cluster mill – multiple backing rolls on smaller rolls
 Tandem rolling mill – sequence of two-high mills

Various configurations of rolling mills: (a) 2-high rolling mill.
Two-High Rolling Mill

Various configurations of rolling mills: (b) 3-high rolling mill.
Three-High Rolling Mill

Various configurations of rolling mills: (c) four-high rolling mill.
Four-High Rolling Mill

Multiple backing rolls allow even smaller roll diameters
Various configurations of rolling mills: (d) cluster mill
Cluster Mill

A series of rolling stands in sequence
Various configurations of rolling mills: (e) tandem rolling
mill.
Tandem Rolling Mill

Thread Rolling
Bulk deformation process used to form threads on
cylindrical parts by rolling them between two dies
 Important commercial process for mass producing
bolts and screws
 Performed by cold working in thread rolling machines
 Advantages over thread cutting (machining):
 Higher production rates
 Better material utilization
 Stronger threads and better fatigue resistance due to
work hardening

Figure 19.6 Thread rolling with flat dies:
Thread Rolling
(1) start of cycle (2) end of cycle

Work Rest
Rolls
Work
piece
Machined thread Rolled thread
Thread Rolling

Forging
Deformation process in which work is
compressed between two dies Oldest of the
metal forming operations, dating from about 5000
B C
 Components: engine crankshafts, connecting
rods, gears, aircraft structural components, jet
engine turbine parts
 Also, basic metals industries use forging to
establish basic form of large parts that are
subsequently machined to final shape and size .
Forging today is done either with presses or with
hammers powered by compressed air, electricity,
hydraulics, or steam.
 Forged parts can now range in weight from less
than a kilogram to 170 metric tons
 Forging can be broken down into two main types;
cold and hot forging

Hot Forging
 Hot forging is defined as working a metal above its
recrystallization temperature.
Advantages Disadvantages
Decrease in yield
strength, which means
that it is easier to work.
Undesirable reactions
between the metal and
the surrounding
atmosphere
Elevated temperatures
increase diffusion
between the metals
Less precise tolerances
due to thermal
contraction and warping
from uneven cooling
Pores may reduce in size
or close completely
during deformation
Grain structure may vary
throughout the metal

Cold Forging
 Cold forging is defined as working a metal below its
recrystallization temperature, but usually around room
temperature.
Advantages Disadvantages
Better surface finish Higher forces are
required
Better reproducibility and
interchangeability
Heavier and more
powerful equipment and
stronger tooling are
required
No Heating required Metal is less ductile and
Undesirable residual
stress may be produced
Directional properties can
be imparted into the
metal
Metal surfaces must be
clean and scale-free

Forging operation
 Drawing out:
 In this operation in which the metal get
elongated with a reduction in the cross sectional
area. For this purpose, the force is applied in
the direction perpendicular to the length of
the axis.
 Upsetting:
In this operation, cross sectional
area of the work piece increases by decreasing
length. For this purpose is force is applied in the
direction parallel to the length of the axis

Types of Forging Dies
 Smith forging: Traditional operation, done by
manual hammering in open dies.
 Drop Forging or Impression : done by
serious of blows by means drop hammers -die
contains cavity or impression that is imparted to
work during this process flash is created.
 Machine forging: in case of drop and press forging the
material would be continuously drawn out where as in
this case only upsetting take place.
 Press forging : similar to the drop forging expect
force is applied continuously (squeezing type).

Drop forging or Impression-Die Forging

Drop forging
 It uses closed impression dies to get the desire shape of the
component.
 The shaping is done by serious of hammering given to the
material to form a desired shape.
 The equipment used for this : Drop hammers.
Apply impact load against work.
 Two types:
 Gravity drop hammers - impact energy from falling weight of a
heavy ram
 Power drop hammers - accelerate the ram by pressurized air or
steam
 Disadvantage: impact energy transmitted through anvil into floor
of building
 Commonly used for impression-die forging
 Die consists of two halves, lower half is fixed where as upper half
is movable.
 The heated stock is placed between the die.

Diagram showing details of a drop hammer for
impression-die forging.
Drop Hammer Details

Drop forging Cont…..
 The required impression are machined in the die.
 During hammering the between the stock is
compressed, because of continuous blows the metal
will completely spread over the die
 Complex shape can be possible.
 Depending upon the requirement of grain shape and
complex shape number of pass will be decided.
 Application: crank, connecting rod, crank shaft and
crane hook.
Disadvantages: in a single stretch it is not possible to
get the final product and huge force will be
transmitted to the building.

Drop forging hammer, fed by conveyor and heating units at
the right of the scene (photo courtesy of Chambersburg
Engineering Company).

Advantages and Limitations
 Advantages of impression-die forging
compared to machining from solid stock:
 Higher production rates
 Less waste of metal
 Greater strength
 Favorable grain orientation in the metal
 Limitations:
 Not capable of close tolerances
 Machining often required to achieve
accuracies and features needed

Press forging
Similar to the drop forging, it uses closed dies. Incase of
drop forging the force will be supplied as a serious of
blows where as in this case the force will be applied
as a squeezing force with the help of hydraulic
operation.
Because of the continuous action of the hydraulic press
the material gets uniformly deformed through out its
entire depth.
Press forging Drop forging
The entire force is transmitted to
the stock or work
The partial forces is transmitted
to the building
The finish obtained in the product
is fine
the finish of the product is not
fine because of its serious blow

Machine forging
 Some times it is called upset forging
 Even though the drop and press forge are done
by machine, historically upsetting process is
called machine forging.
 Normally used for making bolt heads.

Figure 19.23 Examples of heading (upset forging) operations: (a)
heading a nail using open dies, (b) round head formed by punch,
(c) and (d) two common head styles for screws formed by die, (e)
carriage bolt head formed by punch and die.
Heading (Upset Forging)

Figure 19.22 An upset forging operation to form a head on a bolt
or similar hardware item The cycle consists of: (1) wire stock
is fed to the stop, (2) gripping dies close on the stock and the
stop is retracted, (3) punch moves forward, (4) bottoms to
form the head.
Upset Forging

 Other application of upset forging is
 Making of gear, shaft, axles.
 Upsetting machines are in horizontal in nature.
 In this process it is not possible to get the final
shape of the. product in a single pass. It just like
drop forging process.

Upsetting and Heading
Forging process used to form heads on nails, bolts,
and similar hardware products
 More parts produced by upsetting than any other
forging operation
 Performed cold, warm, or hot on machines called
headers or formers
 Wire or bar stock is fed into machine, end is
headed, then piece is cut to length
 For bolts and screws, thread rolling is then used
to form threads

Extrusion
Compression forming process in which work metal
is forced to flow through a die opening to produce
a desired cross-sectional shape
 Process is similar to squeezing toothpaste out of
a toothpaste tube
 In general, extrusion is used to produce long
parts of uniform cross sections
 Two basic types:
 Direct extrusion
 Indirect extrusion

Figure 19.30 Direct extrusion.
Direct Extrusion

Comments on Direct Extrusion
 Also called forward extrusion
 As ram approaches die opening, a small portion
of billet remains that cannot be forced through die
opening
 This extra portion, called the butt, must be
separated from extrudate by cutting it just beyond
the die exit
 Starting billet cross section usually round
 Final shape of extrudate is determined by die
opening

Figure 19.31 (a) Direct extrusion to produce a hollow or semi-hollow
cross sections; (b) hollow and (c) semi-hollow cross sections.
Hollow and Semi-Hollow Shapes

Figure 19.32 Indirect extrusion to produce (a) a solid
cross section and (b) a hollow cross section.
Indirect Extrusion

Comments on Indirect
Extrusion
 Also called backward extrusion and reverse
extrusion
 Limitations of indirect extrusion are imposed by
 Lower rigidity of hollow ram
 Difficulty in supporting extruded product as it exits
die

Advantages of Extrusion
 Variety of shapes possible, especially in hot
extrusion
 Limitation: part cross section must be uniform
throughout length
 Grain structure and strength enhanced in
cold and warm extrusion
 Close tolerances possible, especially in cold
extrusion
 In some operations, little or no waste of
material

Hot vs. Cold Extrusion
 Hot extrusion - prior heating of billet to above its
recrystallization temperature
 Reduces strength and increases ductility of the
metal, permitting more size reductions and more
complex shapes
 Cold extrusion - generally used to produce
discrete parts
 The term impact extrusion is used to indicate high
speed cold extrusion

Extrusion Ratio
Also called the reduction ratio, it is defined as
where rx = extrusion ratio; Ao = cross-sectional
area of the starting billet; and Af = final cross-
sectional area of the extruded section
 Applies to both direct and indirect extrusion
f
o
x
A
A
r 

Figure 19.35 (a) Definition of die angle in direct extrusion; (b)
effect of die angle on ram force.
Extrusion Die Features

Comments on Die Angle
 Low die angle - surface area is large, which
increases friction at die-billet interface
 Higher friction results in larger ram force
 Large die angle - more turbulence in metal flow
during reduction
 Turbulence increases ram force required
 Optimum angle depends on work material, billet
temperature, and lubrication

Orifice Shape of Extrusion Die
 Simplest cross section shape is circular die orifice
 Shape of die orifice affects ram pressure
 As cross section becomes more complex, higher
pressure and greater force are required
 Effect of cross-sectional shape on pressure can
be assessed by means the die shape factor Kx

Figure 19.36 A complex extruded cross section for a heat
sink (photo courtesy of Aluminum Company of America)
Complex Cross Section

 Introduction
 The Extrusion Process
 Extrusion Practice
 Hot Extrusion
 Cold Extrusion
 Impact Extrusion
 Hydrostatic Extrusion

Indirect extrusion and hydrostatic
Extrusion

Important process variables
Process variables in direct extrusion. The die angle, reduction in cross-
section, extrusion speed, billet temperature, and lubrication all affect the
extrusion pressure.

 Extrusion
Hot extrusion Cold
extrusion
1. Forward 1. Forward Hydro static
2. backward 2. Backward (a) Cold
Extrusion
(b) Impact
extrusion

Comparison of forward and
backward
Forward hot extrusion Back ward hot extrusion
Flow of metal in the forward
direction same as that of ram or
plunger
Flow of metal in the forward
direction opposite to the movement
of ram or plunger
Mostly preferred because of its
simple in construction
Not preferred that much because of
complicated construction
The friction force in prevalent in
case of direct extrusion because of
relative movement between billet
and cylinder
In this model it is avoided because
die is connected with ram, no
movement of billet.
This is the advantage of indirect
extrusion.
Extrusion pressure is not uniform
Lubricant is necessary because
while extruding steel material
temperature are high.
Extrusion pressure is uniform
because no movement of billet
material. Lubricant is necessary
because while extruding steel
material temperature are high.
Oil and graphite can be used, if
temp is high molten glass can be
used.
The surface defect is the major
problem, every material would
coming out from the extrusion

Forward cold extrusion
 Similar to the forward extrusion process
 Extrusion ratio are higher in hot forward extrusion
process where as extrusion ratio are very lower in
forward cold extrusion process.
 Since materials are heated at higher temperature
higher extrusion ratio is possible.
 Examples for forward cold extrusion is
Aluminum brackets, cans, shock absorber
cylinder.

Forward extrusion(Hydro static)

Hydro static extrusion
 For special application this kind of process will be
employed.
 Metal is compressed in all direction by a liquid
rather than ram.
 Since liquid is present in the container no need to
have lubricant to cool the process.
 Material will compressed uniformly.
 Gray cast iron material can be extruded(Brittle
material)
 SAE 30 or castor oil with 10 % alcohol, glycerin,
and ethyl alcohol.

Hydro static extrusion Cont……
 The hydro static pressure range from 1110 to
3150 MPa.
 Application:
 Making wires for less ductile material
 Making reactor fuel rods.

Impact extrusion
Most common process for extruding soft materials.
Also called backward extrusion process.
The slug for making the component is kept on the
die and punch strikes the slug.
Because of the impact force, side wall go straight
along the punch.
The height depends upon the height of the slug.
Commonly used for making collapsible tubes and
containers.

Cold extrusion Forging (Backward
extrusion )

Cold extrusion Forging
 Similar to the impact extrusion process.
 The height of the slug will be higher incase of
impact extrusion where as in this case height will
be lower and thickness will be higher.
 In all conventional extrusion process the area of
cross section of the extruded part will be the
same.
 In this case different area cross section can be
possible to made.
 Suitable for non ferrous alloys.

Extruding tubes
 This is also one type of hot extrusion process, for
making tubes.
 Double action ram can be used for making tubes .
 In this model the solid ram moves towards the
billet material and than plunger ram will be moved
to form a complete required shape.

Wire drawing die
 Wire means small diameter and uniform cross
section.
 Rod means

Metal Forming Process

More Related Content

What's hot

Viewers also liked

Similar to Metal Forming Process

Recently uploaded

Metal Forming Process