Forming1

MI-102: Manufacturing Techniques I. I. T. ROORKEE
FORMING PROCESSES
 Forming is a deformation based approach used to give the
desired size and shape.
 Therefore, all factors affecting the deformation tendency
(ductility, yield strength, strain hardening) will eventually affect
the performance of the forming processes.
 In General an increase in the Temperature results in
 Decrease in Strength
 Increase in Ductility
 Decrease in the Rate of Strain Hardening
 All these effects ease of deformation required for forming
 On the basis of forming Temperature forming processes
can classified as
 COLD Forming
 WARM Forming
 HOT Forming

COLD FORMING HOT FORMING
Below their Recrystallization
Temperature
Above their Recrystallization
Temperature
Temperature of Deformation <
0. 3 Melting Temperature on
the Absolute Scale
Temperature of Deformation
> 0.6 Melting Temperature on
the Absolute Scale
Recrystallization Temperature
Varies Greatly with the
Material
 Tin is Near Hot-Working at
Room Temperature while Steel
Require Temp. near 1100o
C
WARM FORMING: Deformation Between 0.3 to 0.6 Times the
Melting Point on the Absolute Scale

Hot Working Cold Working
Processes
Forging
Rolling
 Extrusion
 Hot Drawing
 Piercing
Squeezing: Cold Rolling, Cold
Forging , Cold Extrusion,
Coining, Peening, Burnishing,
and Thread Rolling.
Bending: Angle Bending, Roll
Bending, Roll-forming, and
Straightening.
Shearing: Slitting, Blanking,
Piercing, Notching, Nibbling,
Drawing: Spinning, Embossing,
Stretch Forming, and Ironing
Sheet-metal Forming
Operations

FORGING
 Involves application of force on metal to
cause plastic deformation so as to get the
required final shape.
 Forging is Generally a Hot Working but also
be Cold Forging.
 Forging can be done in two ways
 Drawing Out: Elongates the object with
a Reduction in the Cross-Sectional
Area using Force Applied in a Direction
Perpendicular to the longitudinal Axis.
 Upsetting: increases the Cross-
Sectional Area of the Stock at the
Expense of its Length using Force
Applied in a Direction Parallel to the
Length Axis.
Drawing Out
Upsetting

FORGING TYPES
Smith Forging: Traditional Forging
performed using Open Dies with help of
Manual or Powered Hammers.
 Drop Forging: uses Closed Impression
Dies by Means of Drop Hammers in a
Series of Blows.
 Press Forging: is Similar to Drop Forging
with the Difference that the Force is a
Continuous Squeezing Type.
 Machine Forging: the Material is only
Upset to Get the Desired Shape using a set
of dies.

SMITH FORGING
 Involves Heating the Stock in the Blacksmith's Hearth and
then Beating it Over the Anvil.
 The stock is Manipulated in Between the Blows.
 Used for low volume production of variety of designs.

 The Drop Forging Die Consists of Two Halves.
 The Lower Half is Fixed to the Anvil of the
Machine,
 While the Upper Half of the Die is Fixed to
the Ram.
 The Heated Material Stock is Kept in the
Lower Die while the Ram Delivers Four to
Five Blows on the Material, in Quick
Succession so that the Material Spreads and
Completely Fills the Die Cavity.
 When the Two Die Halves Close, the
Complete Cavity is Formed.
 Since the Machined impressions in the Die
Cavity help to get more Complex Shapes in
Drop Forging as Compared to Smith Forging

Drop forging

 Typical Products Produced by Drop Forging are Crank, Crank
Shaft, Connecting Rod, Wrench, Crane Hook, etc.
 Final Shape Desired in Drop Forging Cannot be Obtained
Directly from the Stock in a Single Pass.
 Depending on the Shape of the Component, and the Desired
Grain Flow Direction, the Material should be Manipulated
in a Number of Passes.

FULLERING IMPRESSION: Reducing Stock to the
Desired Size.
EDGING IMPRESSION (Preforming): Ensures
Defect-Free Flow of Material, Complete Die Fill and
Minimum Flash Loss.
BENDING IMPRESSION: for the Parts having a
Bent Shape.
BLOCKING is a Step before Finishing. The Material
Flows to Deep Pockets, Sharp Corners, etc.
before the Finishing Impression without Flash.
FINISHING: is the Final Impression for Actual
Shape .at this stage a Little Extra Material is
Added to the Stock Forms the Flash and
Surrounds the Forging in the Parting Plane.
TRIMMING is removal of the Extra Flash Present
Around the Forging to make the Forging in Usable
.

 In Press Forging, involves Single Continuous Squeezing
Action results in Uniform Deformation Throughout the
Depth.
 The Impressions Produced in the Press Forging are
Cleaner as Compared to the Jarred Impressions Produced
in the Drop Forged Components.
 Press forging suits for smaller size components than drop
forging as former needs higher Press Capacity for Deforming
in Closed Impression Dies. No such Limitation for Press
Forging in Open Dies.
 Presses Capacities May Range from 5 MN to 50 MN for
Normal Applications and as High as 600 MN for Special
Heavy Duty Applications.
PRESS FORGING

 Initially Developed for Making the Bolt Heads in a
Continuous Fashion.
 Due to Beneficial Grain Flow Obtained in Upsetting, it is Used
for Making Gear Blanks, Shafts, Axles and Similar Parts.
Some Typical Parts Produced by Upset Forgings are Shown in
the Figure.
 The Die Set Consists of a Die and a Corresponding Punch or a
Heading Tool.
MACHINE FORGING

 The Upset Forging Cycle
 Movable Die comes closer to Stationary Die to Grip
the Stock.
 The Two Dies in Closed Position Form the
Necessary Die Cavity.
 The Punch Upsets stock to Fill the Die Cavity.
 After Upsetting, Punch Moves Back to its Position.
 Movable Grippes Release the Stock.
 Similar to Drop Forging, the Upsetting Operation is
Carried Out in a Number of Stages or Passes.
 The Material Stock is Moved from One Stage to the
Other in a Proper Sequence Till the Final Forging is
Ready.
MACHINE FORGING

Some Typical Upset or Machine Forged Components

FORGING DEFECTS
 Unfilled Sections: of Die Cavity by the Flowing Material due to:
 Improper Design of Forging Die or
 Faulty Forging Techniques.
 Cold Shut: A Small Crack at the Corners of the Forging due to
Improper Design of the Die e.g. Corner and Fillet Radii are
Small which in turn results in small cracks due to poor flow of
materials at the Corner.
 Scale Pits: Irregular Depressions on the Surface of the Forging
primarily due to improper Cleaning of the Stock Used for Forging.
 The Oxide and Scale Present on the Stock Surface Gets
Embedded into the Finished Forging Surface. When the Forging
is Cleaned by Pickling, these are Seen as Depressions on the
Forging Surface.

 Die Shift:
CAUSES: Die Shift is Caused by the
 Misalignment of the Two Die Halves
Making the Two Halves of the Forging to
be of Improper Shape.
 Flakes: These are Basically Internal
Ruptures due to poor ductility of surface
layer during deformation caused by Rapid
Cooling

ROLLING
 Rolling is a Process where the Material is Compressed
Between Two Rotating Rolls for Reducing its Cross-
Sectional Area.
 Rolling is Normally a Hot Working Process unless specified
as Cold Rolling.
 At Entry, the Surface Speed of Rolls is Higher than that of
the Incoming Material, whereas the Material Velocity at the
Exit is Higher than that of the Surface Speed of the Rolls
due to difference cross sectional area.

Scheme of Rolling Process

 Rougher Rolls Achieve Greater Reduction than Smoother
Rolls. But, the Rough Roll Surface may Get Embedded into
the Rolled Metal thus Producing Rough Surface.
 The Reduction that could be Achieved with a Given Set of Rolls
is Designated as the Angle of Bite. This Depends on the Type of
Rolling and the Conditions of the Rolls as shown in Table.

ROLLING STAND
2-High Reversing Rolling
Stand:
 Direction of Roll Rotation
can be Reversed these
reduce Handling of the
Hot Material in Between
the Rolling Passes.

3-High Rolling Stand:
 Arrangement is Used for Rolling of Two
Continuous Passes in a Rolling Sequence
without Reversing the Drives.
 A Table-Tilting Arrangement is
Required to Bring the Material to the
Level with the Rolls.

4-High Rolling Stand:
 Backup Rolls for Providing the Necessary Rigidity to the
Small Rolls.

 Since Required Final Shape Cannot be Obtained in
a Single Pass
 The Rolling Mills are Generally need More
than One Pass to other stands or by Reversing
the Roll Direction or
 The Steel Ingot: 600 x 600 mm. These Ingots are
Further Processed in Rolling Mills to Produce the
Intermediate Shapes such as Blooms, Slabs and
Billets.
 Blooms: 150 x 150 mm to 400 x 400 mm
(square).
 Slabs: 500 to 1800 mm and Thickness from
50 to 300 mm (rectangle).
 Billets: from 40 x 40 mm to 150 x 150 mm
(rectangle).

Roll Pass Sequence can be Broadly Categorized into
THREE Types:
1. Break Down Pass:
 Used for Reducing the Cross-Sectional Area
Nearer to what is Desired.
2. Roughing Pass:
 The Cross-Section Gets Reduced, but Shape of
the Rolled Material also Comes Nearer to the
Final Shape.
3. Finishing Pass:
 Gives the Required Shape of the Rolled Section.
ROLL PASSES

DRAUGHT
 If the Cross Section of the Product Before and
After Rolling Process is A x B and a x b Respectively,
DRAFT is Defined as (A + B)- (a + b)
 Roll Pass Schedule can be obtained from
Draught.
 If Mean Draught for Each Pass is Known, then
Number of Passes can be Estimated.
 Draught Provided in Each Pass
also Depends on the
 Work Material,
 Angle of Bite,
 Roll Strength,
 Power of the Rolling Mill,
and
 Condition of the Rolls.

 Draughts of All the Passes in the Rolling
Sequence are NOT the Same.
 The Main Criteria for Choosing the Draught
is the Angle of Bite.
 Lower draught is used in subsequent passes.
 Reason for Reducing Draught in the Later
Passes:
 in Hot Rolling the Reduction in Stock
Thickness which Causes it to Lose Heat
Quickly and thus Increases the Rolling
Load.
 in Cold Rolling, the Strain Hardening of the
Stock Material Necessitates a Reduction in
Draught in the Succeeding Passes.
Selection of draught

EXTRUSION
 In Extrusion Process, the Material is Confined in a Closed Cavity
and then Forced to Flow From Only One Opening so that the
Material Takes the Shape of the Opening.

 Used to Make Components having a Constant Cross-Section
over any Length.
 More Complex Parts can be Obtained by Extrusion than
that of Rolling, as Die become Simple and Easier to
Make.
 Extrusion is a Single Pass Process.
 The Amount of Reduction Possible in Extrusion is Large.
 Generally Brittle Materials can Also be Very Easily Extruded.
Typical
Extrusion
Shapes

 Extrusion Ratio is Defined as the Ratio of
Cross-Sectional Area of the Billet to that of
the Extruded Section.
 Typical Values of the Extrusion Ratio are 20
to 50.
 The Extrusion Pressure for a Given Material
Depends on the
 Extrusion Temperature,
 Reduction in Area, and
 Extrusion Speed

CLASSIFICATION OF EXTRUSION PROCESS

FORWARD HOT EXTRUSION
 The Direction of Flow of Material is the Same as that of the
Ram.
 Friction is Important Because of the Relative Motion
Between the Heated Material Billet and the Cylinder Walls.
 Lubricants are to be used To Reduce this Friction.
Forward Extrusion
 For Low
Temperatures:,
Oil Mixture and
Graphite
 For High
Temperature,
Molten Glass
for Extruding
Steels.

BACKWARD or INDIRECT HOT EXTRUSION
 The Ram Compresses the Material Against the Container,
Forcing the Material to Flow Backwards through the Die
in the Hollow Plunger or Ram.
 Since Billet in the Container Remains Stationary  No
Friction.
Backward Extrusion
 Extrusion Pressure
is Not Affected by
the Length of the
Billet as friction in
absent
 Problem is
imposed by
Handling Extruding
Material Coming
Out through the
Moving Ram.

FORWARD COLD EXTRUSION
 Forward Cold Extrusion is Similar to the Forward Hot
Extrusion Process Except with low Extrusion Ratios and high
Extrusion Pressures.
 Used for Simple Shapes with Better Surface Finish and
Mechanical Properties.
IMPACT EXTRUSION
It is modification of Backward Cold Extrusion Carried Out by
the Impact Force of the Punch.
 Material is Extruded through the Gap Between the Punch
and Die Opposite to the Punch Movement.
 Suitable for Softer Materials such as Aluminum and its
Alloys.
 Used for Making the Collapsible Tubes for Housing Pastes,
Liquids and similar Articles.

Impact Extrusion

COLD EXTRUSION FORGING:
 The Cold Extrusion Forging is Similar to Impact
Extrusion, the
 Main Difference being the Side Walls much Thicker
and with More Height.
 The Component is Ejected by Means of the Ejector Pin
Provided in the Die

HYDROSTATIC EXTRUSION:
 The Material Billet is Compressed from all Sides by
a Liquid Rather than the Ram.
 The Material is Uniformly Compressed from All
Sides throughout the Deformation Zone.
 Consequently Highly Brittle Materials such as
Grey Cast Iron can also be Extruded.
 Commercial Applications of the Hydrostatic
Extrusion are Limited to
 Extrusion of Reactor Fuel Rods,
 Cladding of Metals, and
 Making Wires of Less Ductile Materials.

Hydrostatic Extrusion

WIRE DRAWING
 Wire Drawing is a cold working process to Obtain Wires
from Rods of Bigger Diameter through a Die.
 The End of the Rod is Made into a Point Shape and
Inserted through the Die Opening then Pull the Wire
through the Die with help of griper
 Material to be Wire Drawn should be Sufficiently Ductile.
DRAWING

Wire Drawing Set Up
Various Die Materials Used are Chilled Cast Iron,
Tool Steels, Alloy Steels, Tungsten Carbide and Diamond.

 In Tube Drawing, a Mandrel of the Requisite Diameter is
Used to Form the Internal Hole.
 The Tubes are also First Pointed and then Entered through
the Die where the Point is Gripped in Similar way as the
Wire Drawing and Pulled Through.
TUBE DRAWING

SHEET METAL OPERATIONS
 Metal Sheet: Plates of thickness < 5 mm
 Sheet metal operations use different types
of stresses for processing
 Shear stress is primarily used in sheet
metal processing
Stress Induced Operations
Shearing Shearing, Blanking, Piercing,
Trimming, Shaving, Notching,
Nibbling
Tension Stretch-Forming
Compression Ironing, Coining
Tension and
Compression
Drawing, Spinning, Bending,
Embossing, Forming

SHEARING
 The Sheet IS deformed between two shearing
Blades (developing tensile and compressive stress).
 Then cracks nucleate and grow when material near
cutting edges is elongated beyond fracture limit which
later join for separation.

BLANKING:
 Process of obtaining a small piece of strip by cutting
(shearing from the Stock with help of a Punch.
 The removed strip is Called Blank used for further
processing to get useable product.
Blanking/Punching Die
PUNCHING:
Similar to blanking
except
that objective is to
make Holes in
Sheet
and removed strip is
considered as scrap

WITHOUT
PROPER
GRIPPING
OF SHEET
ROUGH
EDGE

WITH
PROPER
GRIPPING
OF SHEET
CLEAN AND
SMOOTH
EDGE

TRIMMING:
 Removing Small Amount of Extra Material Spread Out Near
the Parting Plane such as Drop Forging and Die Casting.
SHAVING
 Removal of the Burrs Generated during the Shearing Process
in the Blanking or Punching Operation so as to achieve the
Close Tolerance Work.
NIBBLING:
 Removing the Material in Small Increments to Cut a Specific
Contour on a Sheet using repeating Punching.
 Nibbling is Used When the Contour is Long and a Separate
Punch is Impractical and Uneconomical.
NOTCHING: Cutting a Specified Small Portion of Material
Towards the Edge of the Material Stock.

STRETCH-FORMING
 The Sheet is Clamped at ends and Stretched over the
Die so as to achieve plastic State and permanent
deformation.
SHEET METAL OPERATIONS INVOLVING
TENSION

Stretch forming

IRONING
It involves thinning and lengthening of the wall
of material by generating compressive stress
between the Die and Punch having using the
Clearance (spacing) finer than the Drawing
Operation.
 Up to 50%
thinning can
be obtained in
a Single
Ironing
Operation
Ironing Operation
SHEET METAL OPERATIONS INVOLVING COMPRESSION

COINING
 It is just like a Cold Forging Operation except that the
Flow of the Material Occurs Only at the Top Layers
and NOT in the Entire Volume.
 The Punch and Die have Engraved Details Required on
Both Sides of the Final Object and uses high pressure
(1600 MPa) to get Fine Details on the Surface.
 For Making
Coins, Medals
& Impressions
on Decorative
Items

DRAWING/DEEP DRAWING
 Drawing is the Process of Making Cups (high < half
diameter), and similar product, from Metal Blanks.
 When the Cup Height is More than Half the Diameter, the
Drawing Process is known as Deep Drawing.
SHEET METAL OPERATIONS INVOLVING
TENSION and COMPRESSION

Blank Holding in
Deep Drawing

SPINNING
 Used for Making Axi-Symmetrical Cup Shaped Articles.
 Force (moving) is Applied on the Rotating Blank is Held
Against the Form Block so as get Shape of the Form Block
(of wood).

BENDING
 Operation of Deforming a Flat Sheet Around a Straight
Axis at the Neutral Plane.
 When material is subjected to plastic deformation, the
Neutral Axis Moves Downward due to differential strain
on both sides of neutral axis as the Materials Oppose
Compression in much Better way than Tension.
 Nomenclature of Bending and Type of Bending Methods
are Shown in Following Figures.

Nomenclature of Bending

Type of Bending Methods

EMBOSSING
 An Operation for Making Raised Figures/letter on
Sheets with its Corresponding Relief on the Other Side.
 The Process Involves Drawing and Bending of the
Material.
 Generally Used for increasing the Rigidity by localized
deformation and for Decorative Sheet Work.

Forming1

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