Metal Forming Processes

Metal Forming Processes

1. Manufacturing Process - I

UNIT –II
Metal Forming Processes


Prepared By
Prof. Shinde Vishal Vasant
Assistant Professor
Dept. of Mechanical Engg.
NDMVP’S Karmaveer Baburao Thakare
College of Engg. Nashik
Contact No- 8928461713
E mail:- [email protected]
Website:- www.vishalshindeblog.wordpress.com

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2. Introduction
•Practically all metals, which are not used in cast form are
reduced to some standard shapes for subsequent processing.
•Manufacturing companies producing metals supply metals
in form of ingots which are obtained by casting liquid metal
into a square cross section.
•Slab (500-1800 mm wide and 50-300 mm thick)
•Billets (40 to 150 sq mm)
•Blooms (150 to 400 sq mm)
•Sometimes continuous casting methods are also used to cast
the liquid metal into slabs, billets or blooms.
•These shapes are further processed through hot rolling,
forging or extrusion, to produce materials in standard form
such as plates, sheets, rods, tubes and structural sections.
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3. Sequence of operations for obtaining
different shapes
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5. Metal forming processes
•Large group of manufacturing processes in which
plastic deformation is used to change the shape of
metal work pieces
•The tool, usually called a die, applies stresses that
exceed the yield strength of the metal
–The metal takes a shape determined by the
geometry of the die

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6. Basic Types of
Metal Forming Processes
1.Bulk deformation
–Rolling processes
–Forging processes
–Extrusion processes
–Wire and bar
drawing
2.Sheet metalworking
–Bending operations
–Deep or cup
drawing
–Shearing processes
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7. Temperature in Metal Forming
•Any deformation operation can be accomplished with
lower forces and power at elevated temperature
•Three temperature ranges in metal forming:
–Cold working
–Warm working
–Hot working
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8. Hot and cold working processes
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9. Cold Working
•Performed at room temperature or slightly
above
•Many cold forming processes are important
mass production operations
•Minimum or no machining usually required
–These operations are near net shape or net
shape processes
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10. Advantages of Cold Forming
•Better accuracy, closer tolerances
•Better surface finish
•Strain hardening increases strength and
hardness
•Grain flow during deformation can cause
desirable directional properties in product
•No heating of work required
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11. Disadvantages of Cold Forming
•Higher forces and power required for
deformation
•Surfaces of starting work must be free of scale
and dirt
•Ductility and strain hardening limit the amount
of forming that can be done
–In some cases, metal must be annealed before further
deformation can be accomplished
–In other cases, metal is simply not ductile enough to be
cold worked
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12. Hot Working
•Deformation at temperatures above the re crystallization
temperature.
•The process of formation of new grains is called
recrystallisation process and corresponding temperature is
called recrystallisation temperature
–Recrystallization temperature = about one-half of melting
point on absolute scale
•In practice, hot working usually performed somewhat
above 0.5T
m
•Metal continues to soften as temperature increases
above 0.5T
m, enhancing advantage of hot working
above this level
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13. Advantages of Hot Working
•Work piece shape can be significantly altered
•Lower forces and power required
•Metals that usually fracture in cold working can
be hot formed
•Strength properties of product are generally
isotropic
•No strengthening of part occurs from work
hardening
–Advantageous in cases when part is to be subsequently
processed by cold forming
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14. Disadvantages of Hot Working
•Lower dimensional accuracy
•Higher total energy required, which is the sum
of
–The thermal energy needed to heat the workpiece
–Energy to deform the metal
•Work surface oxidation (scale)
–Thus, poorer surface finish
•Shorter tool life
–Dies and rolls in bulk deformation
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15. Hot working operations
•Forging
•Rolling
•Welding
•Extrusion
•Spinning
•Hot piercing and rolling
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16. Cold working operations
•Cold rolling
•Extrusion
•Pressing
•Deep drawing
•Squeezing
•Bending
•Shearing

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17. Bulk Deformation Processes
Rolling: Compressive deformation process in which the thickness of a
plate is reduced by squeezing it through two rotating cylindrical
rolls.

Forging: The work piece is compressed between two opposing dies so
that the die shapes are imparted to the work.

Extrusion: The work material is forced to flow through a die opening
taking its shape

Drawing: The diameter of a wire or bar is reduced by pulling it through
a die opening (bar drawing) or a series of die openings (wire
drawing)
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18. Basic bulk deformation processes: (a) rolling (b) Forging
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19. Basic bulk deformation processes: (c) extrusion (d) Drawing
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20. Sheet Metal working
•Forming and related operations performed on
metal sheets, strips, and coils
•High surface area-to-volume ratio of starting
metal, which distinguishes these from bulk
deformation
•Often called press working because presses
perform these operations
–Parts are called stampings
–Usual tooling: punch and die
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21. Basic sheet metalworking operations: (a) bending (b) Drawing
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22. Basic sheet metalworking operations: (c) shearing
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23. Comparison of Hot and Cold Working
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Sr.
No
Hot Working Cold Working
1 Working above
recrystallization temperature
Working below recrystallization
temperature
2 Formation of new crystals (Grains) No crystal formation (Grains)
3 Surface finish not good Surface finish is good
4 No stress formation Internal Stress developed
5 Improved Mechanical Property due
to grain formation
Leads to distortion of metal
grains
6 Closed dimensional tolerances
cannot be maintained
Superior dimensions can be
obtained
7 Improves some mechanical
properties like impact strength and
elongation
During process, strength and
elongation decreases

24. Friction in Metal Forming
•In most metal forming processes, friction is
undesirable:
–Metal flow is retarded
–Forces and power are increased
–Wears tooling faster
•Friction and tool wear are more severe in hot working
•if the co efficient of friction is very high, that
condition is called as sticking or sticking friction
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25. Lubrication in Metal Forming
•Metal working lubricants are applied to tool-work
interface in many forming operations to reduce
harmful effects of friction
•Lubricant for cold working processes are mineral oil,
fats and fatty oils, soaps
•Lubricants for hot working processes are mineral
oils, graphite, moltan glass etc

•Benefits:
–Reduced sticking, forces, power, tool wear
–Better surface finish
–Removes heat from the tooling

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26. Hot rolling
•Deformation process in which work thickness is
reduced by compressive forces exerted by two
opposing rolls
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27. •The cross section of the work piece is reduced by the
process. The material gets squeezed between a pair of
rolls, as a result of which the thickness gets reduced
and the length gets increased.
•Mostly, rolling is done at high temperature, called hot
rolling because of requirement of large deformations.
Hot rolling results in residual stress-free product.
•Bloom is has a square cross section, with area more
than 230 cm2. A slab, also from ingot, has rectangular
cross-section, with area of at least 100 cm2 and width
at least three times the thickness. A billet is rolled out of
bloom, has at least 40 mm X 40 mm cross-section.
•Blooms are used for rolling structural products such as
I-sections, channels, rails etc. Billets are rolled into
bars, rods. Bars and rods are raw materials for
extrusion, drawing, forging, machining etc. Slabs are
meant for rolling sheets, strips, plates etc.
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28. Types of rolling mills
•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
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29. ARRANGEMENTS OF ROLLERS
USED IN ROLLING MILLS
TWO HIGH MILL
THREE HIGH MILL
The stock is
returned to the
entrance for
further reduction.
Consist of upper and
lower driven rolls and
a middle roll, which
rotates by friction.
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30. CLUSTER ROLLING MILLS
FOUR HIGH MILL
Small-diameter rolls
(less strength &
rigidity) are
supported by
larger-diameter
backup rolls
Each of the work
rolls is supported
by two backing
rolls.
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31. •Tandem rolling mill – sequence of two-high
mills
•A series of rolling stands in sequence.
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32. Forging process
•Forging is a process in which the work piece is shaped
by compressive forces applied through various dies and
tools. It is one of the oldest metalworking operations.
Most forgings require a set of dies and a press or a
forging hammer.
•Unlike rolling operations, which generally produce
continuous plates, sheets, strip, or various structural
cross-sections, forging operations produce discrete
parts.
•Typical forged products are bolts and rivets, connecting
rods, shafts for turbines, gears, hand tools, and
structural components for machinery, aircraft, railroads
and a variety of other transportation equipment.
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33. •Depending upon complexity of the part forging is carried out as open
die forging and closed die forging.
•In open die forging, the metal is compressed by repeated blows by a
mechanical hammer and shape is manipulated manually.
•In closed die forging, the desired configuration is obtained by
squeezing the work piece between two shaped and closed dies.
•On squeezing the die cavity gets completely filled and excess material
comes out around the periphery of the die as flash which is later
trimmed.
• Press forging and drop forging are two popular methods in closed die
forging.
•In press forging the metal is squeezed slowly by a hydraulic or
mechanical press and component is produced in a single closing of die,
hence the dimensional accuracy is much better than drop forging.
•Both open and closed die forging processes are carried out in hot as
well as in cold state.


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35. Open-Die Forging
•Compression of work piece between two flat dies
•Deformation operation reduces height and increases
diameter of work
•Common names include upsetting or upset forging or
cogging
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36. Open-Die Forging with No Friction
•If no friction occurs between work and die surfaces,
then homogeneous deformation occurs, so that radial
flow is uniform throughout work piece height
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Fig:- Homogeneous deformation of a cylindrical work part
1. start of process with work piece at its original length and
diameter, 2. partial compression, 3. final size.

37. Open-Die Forging with Friction
•Friction between work and die surfaces constrains
lateral flow of work, resulting in barreling effect.
•In hot open-die forging, effect is even more pronounced
due to heat transfer at and near die surfaces, which
cools the metal and increases its resistance to
deformation
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38. Impression-Die Forging or closed die forging
•Compression of work part by dies with inverse of desired part
shape
•Flash is formed by metal that flows beyond die cavity into small
gap between die plates
•Flash serves an important function:
 As flash forms, friction resists continued metal flow into gap,
constraining material to fill die cavity
In hot forging, metal flow is further restricted by cooling against
die plates
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39.  Trimming operation (shearing process) to remove the flash after
impression-die forging.
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40. 28/07/2016
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Sr.
No
Open Die forging Closed die forging
1 In this method, the work piece is
compressed between two flat dies
Work piece is compressed
between two impressed dies
2 Cost of dies are low Higher cost
3 The process is simple process is complex

4 No stress formation Residual stress formation takes
place
5 During process, poor utilization of
metals
Better utilization
6 After the process, machining of
component is required
Machining of component is not
required
7 Dimensional accuracy is not good Dimensional accuracy is good

8 Suitable only for production of
simple component
Simple and complex component

41. Extrusion
•A plastic deformation process in which metal is forced under
pressure to flow through a single, or series of dies until the
desired shape is produced.
•Process is similar to squeezing toothpaste out of a toothpaste tube
•In general, extrusion is used to produce long parts of uniform
cross sections
•Typical products made by extrusion are railings for sliding doors,
tubing having carious cross-sections, structural and architectural
shapes, door and windows frames.
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42. Types
(1)Direct Extrusion (Forward Extrusion)
(2)Indirect Extrusion (Backward Extrusion)
(3)Cold Extrusion
(4)Hot Extrusion
•Direct Extrusion
• Billet is placed in a chamber and forced through a die opening
by a hydraulically-driven ram or pressing stem.
•Dies are machined to the desired cross-section
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44. •Indirect Extrusion
•Metal is forced to flow through the die in an opposite
direction to the ram’s motion.
•Lower extrusion force as the work billet metal is not
moving relative to the container wall.
•Limitations
•Lower rigidity of hollow ram
•Difficulty in supporting extruded product as it exits die
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45. Drawing
•Commonly used to make wires from round bars
•Large quantities of wires, rods, tubes and other sections are
produced by drawing process which is basically a cold
working process.
•In this process the material is pulled through a die in order to
reduce it to the desired shape and size.
•In a typical wire drawing operation, once end of the wire is
reduced and passed through the opening of the die, gripped
and pulled to reduce its diameter.
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46. •Drawing is an operation in which the cross-section of
solid rod, wire or tubing is reduced or changed in shape
by pulling it through a die. Drawn rods are used for
shafts, spindles, and small pistons and as the raw material
for fasteners such as rivets, bolts, screws.
•Drawing also improves strength and hardness when these
properties are to be developed by cold work and not by
subsequent heat treatment.
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47. •Wire drawing machines consisting of multiple draw
dies (typically 4 to 12) separated by accumulating
drums
Each drum (capstan) provides proper force to draw
wire stock through upstream die
Each die provides a small reduction, so desired
total reduction is achieved by the series
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48. •Die Materials
Commonly used materials are Tool Steels and
Carbides
Diamond dies are used for fine wire.
For improved wear resistance, steel dies may be
chromium plated, and carbide dies may be coated
with titanium nitride
For Hot drawing, cast-steel dies are used
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49. Tube drawing
•Tube drawing is also similar to wire drawing, except that a
mandrel of appropriate diameter is required to form the
internal hole.
•The process reduces the diameter and thickness of the tube.
•Tube drawing is very similar to bar drawing, except the
beginning stock is a tube. It is used to decrease the diameter,
improve surface finish and improve dimensional accuracy.
•A mandrel may or may not be used depending on the
specific process used.
•Here two arrangements are shown in figure (a) with a
floating plug and (b) with a moving mandrel

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50. Tube Drawing
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