1. MODULE 3
 COURSE OUTCOMES
 Rolling
 Forging
 Extrusion
 Wire and bar drawing

2. Metal Forming Processes
Rolling Forging
Bending Cup Drawing
Wire Drawing
Extrusion Shearing
Bulk Deformation Processes Sheet Metal Processes

3. Plastic Deformation Processes
Operations that induce shape changes on the work piece by plastic
deformation under forces applied by various tools and dies.
Bulk Deformation Processes
These processes involve large amount of plastic deformation.
The cross-section of workpiece changes without volume change.
The ratio cross-section area/volume is small.
Performed as cold, warm, and hot working operations

5. Cold working performed at room temp.
Advantages: better accuracy, better surface finish, high
strength and hardness of the part, no heating is required.
Disadvantages: higher forces and power, limitations to the
amount of forming, additional annealing for some material is
required, and some material are not capable of cold working.
Warm working performed temp. above the room temp. but
bellow the recrystallization one.
Advantages: lower forces and power, more complex part
shapes, no annealing is required.
Disadvantages: some investment in furnaces is needed.

6. Hot working involves deformation of preheated
material at temp. above the re crystallization temp.
Advantages: big amount of forming is possible,
lower forces and power are required, forming of
materials with low ductility, no work hardening and
therefore, no additional annealing is required.
Disadvantages: lower accuracy and surface finish,
higher production cost, and shorter tool life.

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

9. The Rolls
The rotating rolls perform two main functions:
• Pull the work into the gap between them by
friction between work-part and rolls
• Simultaneously squeeze the work to reduce
cross section

10. Types of Rolling
• Based on work piece 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

11. Some of the steel products made in a rolling mill

12. Flat rolling and its analysis
R = roller radius
p = roll pressure
L = contact length
θ = contact angle
vr = roll speed
to = initial plate
thickness
tf = final plate thickness
vo = plate entry speed
vf = plate exit speed
Side view of flat rolling, indicating before and after thicknesses,
work velocities, angle of contact with rolls, and other features.

13. Flat rolling and its analysis
• The work enters the gap between the rolls at a velocity vo and
exits at a velocity vf. Because the volume flow rate is constant
and the thickness is decreasing, vf should be larger than vo.
• The roll surface velocity vr is larger than vo and smaller than vf.
This means that slipping occurs between the work and the rolls.
• Only at one point along the contact length, there is no slipping
(relative motion) between the work and the roll. This point is
called the “Neutral Point” or the “No Slip Point”.

14. Flat rolling and its analysis
• In flat rolling, the work is squeezed between two rolls
so that its thickness is reduced by an amount called
the draft:
d to tf
where
d: draft
to: starting thickness
tf : final thickness

15. Flat rolling and its analysis
• Rolling may not be possible (the sheet will not be pulled) if the
draft is large. The maximum draft for successful rolling per pass
is:
2
d max R
Where:
dmax : maximum draft successful rolling per pass
μ : coefficient of friction
R : roll radius
to tf
Number of passes 2
R

16. Example:- A series of cold rolling operations is to be used to reduce
the thickness of a plate from 50 mm down to 25 mm in a reversing two
high mill. Roll diameter =700 mm and coefficient of friction between
rolls and work = 0.15. The specification is that the draft is to be equal
on each pass.
Determine (a) minimum number of passes required, and
(b) draft for each pass.
Solution
to tf 50 - 25
number of passes 2 2
3.17 4 passes
R 0 . 15 350
to tf 50 - 25
Draft per pass 6.25 mm
number of passes 4

17. The Flat-rolling Process:
Roll Force, Torque, and Power Requirements
• Rolls apply pressure on the flat strip to reduce its
thickness, resulting in a roll force, F
• Roll force in flat rolling can be estimated from
L = roll-strip contact length
F LwY avg
w = width of the strip
Yavg = average true stress of the strip
2 FLN
• Total power (for two rolls) is Power (in kW)
60 , 000
Roll strip contact length (L ) =
R (h0 hf )
w= Width of the strip
Y avg= Average true stress
N= Speed of the roll in RPM

18. Flat rolling and its analysis
From the previous equations we can conclude the following:
1. The contact length decreases by decreasing the roll radius.
2. The roll force depends on the contact length, and therefore,
reducing the roll radius will reduce the roll force.
3. The torque and power depend on the roll force and contact
length, and therefore, reducing the roll radius will reduce
both the torque and power.
4. The power also depends on the rotational speed of the rolls,
and therefore, reducing the rolls RPM will reduce the
power.

19. Various configurations of rolling mills
(a) 2-high rolling mill
(b) 3-high rolling mill

20. Various configurations of rolling mills
(c) four high rolling mill (d) cluster mill

21. Various configurations of rolling mills
(e) tandem rolling mill

22. Shape-Rolling Operations
• Various shapes can be produced by shape rolling
– Bars
– Channels
– I-beams
– Railroad rails
• Roll-pass design requires considerable experience in
order to avoid external and internal defects

23. Stages in Shape Rolling of an H-section part. Various other structural
sections such as channels and I-beams, are rolled by this kind of
process.

24. Thread Rolling
Bulk deformation process used to form threads on cylindrical parts
by rolling them between two dies
• Most 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 due to work hardening
– Better fatigue resistance due to compressive stresses
introduced by rolling

25. Thread Rolling
Thread rolling with flat dies:
(1) start of cycle, and (2) end of cycle

27. Ring Rolling
Deformation process in which a thick-walled ring of smaller diameter
is rolled into a thin walled ring of larger diameter
• As thick-walled ring is compressed, deformed metal elongates,
causing diameter of ring to be enlarged
• Hot working process for large rings and cold working process for
smaller rings
• Applications: ball and roller bearing races, steel tires for railroad
wheels, and rings for pipes, pressure vessels, and rotating
machinery
• Advantages: material savings, ideal grain orientation,
strengthening through cold working

28. Ring Rolling
Ring rolling used to reduce the wall thickness and increase
the diameter of a ring:
(1) start, and (2) completion of process

29. 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
• In addition, basic metals industries use forging to establish basic
form of large components that are subsequently machined to final
shape and size

30. Classification of Forging Operations
• Cold vs. hot forging:
– Hot or warm forging – most common, due to the
significant deformation and the need to reduce
strength and increase ductility of work metal
– Cold forging - advantage is increased strength that
results from strain hardening
• Impact vs. press forging:
– Forge hammer - applies an impact load
– Forge press - applies gradual pressure

31. Types of Forging Dies
1. Open die forging - work is compressed between two flat
dies, allowing metal to flow laterally without constraint
2. Impression die forging - die surfaces contain a cavity or
impression that is imparted to work part, thus
constraining metal flow - flash is created
3. Flash less forging - work part is completely constrained
in die and no excess flash is produced

32. 1. Open Die Forging
Compression of work part with cylindrical cross-section between
two flat dies
• Similar to compression test
• Deformation operation reduces height and increases diameter
of work
• Common names include upsetting or upset forging

33. LIMITATIONS OF OPEN DIE FORGING
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

34. 2. Impression Die Forging
Compression of work part by dies with inverse of
desired part shape
– 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.

35. Stages in Impression-die (Closed-Die) Forging

36. Impression Die Forging
Advantages and Limitations
• Advantages compared to machining from solid
stock:
– Higher production rates
– Conservation of metal (less waste)
– Greater strength
– Favorable grain orientation in the metal
• Limitations:
– Not capable of close tolerances
– Machining often required to achieve accuracies and features
needed, such as holes, threads, and mating surfaces that fit
with other components

37. 3. Flash less Forging
Compression of work in punch and die tooling whose cavity does allow for
flash
• Starting work part volume must equal die cavity volume within very close
tolerance
• Process control more demanding than impression die forging
• Best suited to part geometries that are simple and symmetrical
• Often classified as a precision forging process
Flash less forging:
(1) just before initial contact with work piece,
(2) partial compression, and
(3) final punch and die closure

38. Forging Hammers (Drop Hammers)
• Apply an impact load against work part - 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
• Most commonly used for impression-die forging
Diagram showing details of a drop hammer for impression die
forging

39. Forging Presses
• Apply gradual pressure to accomplish
compression operation - types:
– Mechanical presses - converts rotation of
drive motor into linear motion of ram
– Hydraulic presses - hydraulic piston actuates
ram
– Screw presses - screw mechanism drives
ram

40. Extrusion
Compression forming process in which the 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 of extrusion:
– Direct extrusion
– Indirect extrusion
Direct extrusion

41. 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 extruded product
by cutting it just beyond the die exit
• Starting billet cross section usually round, but final shape is determined by die
opening
(a) Direct extrusion to produce a hollow or semi hollow cross-section; (b) hollow
and (c) semi hollow cross- sections

42. Comments on Indirect Extrusion
• Also called backward extrusion and reverse extrusion
• Limitations of indirect extrusion are imposed by the lower rigidity of
hollow ram and difficulty in supporting extruded product as it exits die
Indirect extrusion to produce
(a) a solid cross-section and (b) a hollow cross-section

43. General 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

44. Hot vs. Cold Extrusion
• Hot extrusion - prior heating of billet to
above its recrystallization temperature
– This 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

45. A complex extruded cross-section for a heat sink
(photo courtesy of Aluminum Company of America)

46. Wire and Bar Drawing
Cross-section of a bar, rod, or wire is reduced by pulling it through a die
opening
• Similar to extrusion except work is pulled through die in drawing (it is
pushed through in extrusion)
• Although drawing applies tensile stress, compression also plays a
significant role since metal is squeezed as it passes through die opening
Drawing of bar, rod, or wire

47. Wire Drawing vs. Bar Drawing
• Difference between bar drawing and
wire drawing is stock size
– Bar drawing - large diameter bar and rod
stock
– Wire drawing - small diameter stock - wire
sizes down to 0.03 mm (0.001 in.) are
possible
• Although the mechanics are the same,
the methods, equipment, and even
terminology are different

48. Drawing Practice and Products
• Drawing practice:
– Usually performed as cold working
– Most frequently used for round cross-sections
• Products:
– Wire: electrical wire; wire stock for fences, coat
hangers, and shopping carts
– Rod stock for nails, screws, rivets, and springs
– Bar stock: metal bars for machining, forging, and
other processes

49. Wire Drawing
• Continuous 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
– Annealing sometimes required between dies
49
Continuous drawing of wire

50. Bar Drawing
• Accomplished as a single draft
operation - the stock is pulled through
one die opening
• Beginning stock has large diameter and
is a straight cylinder
• This necessitates a batch type operation
Hydraulically operated draw bench for
drawing metal bars