Four Basic Bulk Deformation Four Basic Bulk Deformation ProcessesProcesses

1.1. Rolling – slab or plate is squeezed between Rolling – slab or plate is squeezed between opposing rollsopposing rolls

2.2. Forging – work is squeezed and shaped between Forging – work is squeezed and shaped between opposing diesopposing dies

3.3. Extrusion – work is squeezed through a die Extrusion – work is squeezed through a die opening, thereby taking the shape of the openingopening, thereby taking the shape of the opening

4.4. Wire and bar drawing – diameter of wire or bar is Wire and bar drawing – diameter of wire or bar is reduced by pulling it through a die openingreduced by pulling it through a die opening

Deformation process in which work thickness Deformation process in which work thickness is reduced by compressive forces exerted by is reduced by compressive forces exerted by two opposing rolls two opposing rolls

The rolling process (specifically, flat rolling).

Rolling

Rolls Rolls

Rotating rolls perform two main functions:Rotating rolls perform two main functions:

Pull the work into the gap between them Pull the work into the gap between them by friction between workpart and rollsby friction between workpart and rolls

Simultaneously squeeze the work to Simultaneously squeeze the work to reduce its cross section reduce its cross section

Types of RollingTypes of Rolling Based on workpiece geometry :Based on workpiece geometry :

Flat rolling - used to reduce thickness of a Flat rolling - used to reduce thickness of a rectangular cross section rectangular cross section

Shape rolling - square cross section is Shape rolling - square cross section is formed into a shape such as an I‑beam formed into a shape such as an I‑beam

Based on work temperature :Based on work temperature : Hot Rolling – most common due to the Hot Rolling – most common due to the

large amount of deformation requiredlarge amount of deformation required Cold rolling – produces finished sheet and Cold rolling – produces finished sheet and

plate stock plate stock

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

Rolled Products Made of Steel

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

Diagram of Flat Rolling

Shape RollingShape Rolling

Work is deformed into a contoured cross Work is deformed into a contoured cross section rather than flat (rectangular)section rather than flat (rectangular)

Accomplished by passing work through Accomplished by passing work through rolls that have the reverse of desired shape rolls that have the reverse of desired shape

Products include: Products include: Construction shapes such as I‑beams, Construction shapes such as I‑beams,

L‑beams, and U‑channelsL‑beams, and U‑channels Rails for railroad tracksRails for railroad tracks Round and square bars and rodsRound and square bars and rods

A rolling mill A rolling mill for hot flat for hot flat rolling. The rolling. The steel plate is steel plate is seen as the seen as the glowing strip glowing strip in lower left in lower left corner.corner.

Rolling MillsRolling Mills Equipment is massive and expensiveEquipment is massive and expensive Rolling mill configurations:Rolling mill configurations:

Two-high – two opposing rollsTwo-high – two opposing rolls Three-high – work passes through rolls in Three-high – work passes through rolls in

both directionsboth directions Four-high – backing rolls support smaller Four-high – backing rolls support smaller

work rollswork rolls Cluster mill – multiple backing rolls on Cluster mill – multiple backing rolls on

smaller rolls smaller rolls Tandem rolling mill – sequence of two-high Tandem rolling mill – sequence of two-high

mills mills

Various configurations of rolling mills: (a) Various configurations of rolling mills: (a) 2‑high rolling mill. 2‑high rolling mill.

Two-High Rolling Mill

Various configurations of rolling mills: (b) 3‑high rolling Various configurations of rolling mills: (b) 3‑high rolling mill.mill.

Three-High Rolling Mill

Various configurations of rolling mills: (c) Various configurations of rolling mills: (c) four‑high rolling mill. four‑high rolling mill.

Four-High Rolling Mill

Multiple backing rolls allow even smaller roll diameters Multiple backing rolls allow even smaller roll diameters

Various configurations of rolling mills: (d) cluster mill

Cluster Mill

A series of rolling stands in sequenceA series of rolling stands in sequence

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

Tandem Rolling Mill

ForgingForging Deformation process in which work is Deformation process in which work is

compressed between two dies compressed between two dies Components: engine crankshafts, Components: engine crankshafts,

connecting rods, gears, aircraft structural connecting rods, gears, aircraft structural components, jet engine turbine parts components, jet engine turbine parts

Also, basic metals industries use forging Also, basic metals industries use forging to establish basic form of large parts that to establish basic form of large parts that are subsequently machined to final shape are subsequently machined to final shape and size and size

Classification of Forging OperationsClassification of Forging Operations

Based on Temperature:Based on Temperature: 1) Hot Forging 2) Cold Forging1) Hot Forging 2) Cold Forging

Based on the Die:Based on the Die: 1) Open Die Forging 1) Open Die Forging 2) Impression Die Forging2) Impression Die Forging 3) Flash less Die Forging3) Flash less Die Forging

Based on the applying Pressure:Based on the applying Pressure: Forge hammer - applies an impact load Forge hammer - applies an impact load Forge press - applies gradual pressure Forge press - applies gradual pressure

Types of Forging DiesTypes of Forging Dies

Open‑die forging - work is compressed Open‑die forging - work is compressed between two flat dies, allowing metal to between two flat dies, allowing metal to flow laterally with minimum constraintflow laterally with minimum constraint

Impression‑die forging - die contains cavity Impression‑die forging - die contains cavity or impression that is imparted to workpartor impression that is imparted to workpart Metal flow is constrained so that flash is Metal flow is constrained so that flash is

created created

Flash less forging - workpart is completely Flash less forging - workpart is completely constrained in dieconstrained in die No excess flash is created No excess flash is created

open‑die forging. open‑die forging.

Open-Die Forging

impression‑die forging. impression‑die forging.

Impression-Die Forging

Flashless forging. Flashless forging.

Flashless Forging

Open‑Die Forging Open‑Die Forging

Compression of workpart between two flat Compression of workpart between two flat dies dies

Similar to compression test when workpart Similar to compression test when workpart has cylindrical cross section and is has cylindrical cross section and is compressed along its axiscompressed along its axis Deformation operation reduces height and Deformation operation reduces height and

increases diameter of work increases diameter of work Common names include Common names include upsettingupsetting or or upset upset

forgingforging

Homogeneous deformation of a cylindrical workpart under Homogeneous deformation of a cylindrical workpart under ideal conditions in an open‑die forging operation: (1) start ideal conditions in an open‑die forging operation: (1) start of process with workpiece at its original length and of process with workpiece at its original length and diameter, (2) partial compression, and (3) final size.diameter, (2) partial compression, and (3) final size.

Open-Die Forging with No Friction

Open-Die Forging with FrictionOpen-Die Forging with Friction

Friction between work and die surfaces Friction between work and die surfaces constrains lateral flow of work, resulting in constrains lateral flow of work, resulting in barreling effectbarreling effect

In hot open-die forging, effect is even In hot open-die forging, effect is even more pronounced due to heat transfer at more pronounced due to heat transfer at and near die surfaces, which cools the and near die surfaces, which cools the metal and increases its resistance to metal and increases its resistance to deformation deformation

Actual deformation of a cylindrical workpart in open‑die forging, Actual deformation of a cylindrical workpart in open‑die forging, showing pronounced showing pronounced barrelingbarreling: (1) start of process, (2) partial : (1) start of process, (2) partial deformation, and (3) final shape.deformation, and (3) final shape.

Open-Die Forging with Friction

Impression‑Die ForgingImpression‑Die Forging

Compression of workpart by dies with Compression of workpart by dies with inverse of desired part shape inverse of desired part shape

Flash is formed by metal that flows beyond Flash is formed by metal that flows beyond die cavity into small gap between die die cavity into small gap between die plates plates

Flash must be later trimmed, but it serves Flash must be later trimmed, but it serves an important function during compression:an important function during compression:

Sequence in impression‑die forging: (1) Sequence in impression‑die forging: (1) just prior to initial contact with raw just prior to initial contact with raw workpiece, (2) partial compression, and (3) workpiece, (2) partial compression, and (3) final die closure, causing flash to form in final die closure, causing flash to form in gap between die plates.gap between die plates.

Impression-Die Forging

Advantages and LimitationsAdvantages and Limitations Advantages of impression-die forging Advantages of impression-die forging

compared to machining from solid compared to machining from solid stock:stock: Higher production ratesHigher production rates Less waste of metalLess waste of metal Greater strengthGreater strength Favorable grain orientation in the metalFavorable grain orientation in the metal

Limitations:Limitations: Not capable of close tolerancesNot capable of close tolerances Machining often required to achieve Machining often required to achieve

accuracies and features neededaccuracies and features needed

Flashless ForgingFlashless Forging(Precision Forging)(Precision Forging)

Compression of work in punch and die tooling Compression of work in punch and die tooling whose cavity does not allow for flashwhose cavity does not allow for flash

Starting workpart volume must equal die Starting workpart volume must equal die cavity volume within very close tolerance cavity volume within very close tolerance

Process control more demanding than Process control more demanding than impression‑die forging impression‑die forging

Best suited to part geometries that are simple Best suited to part geometries that are simple and symmetrical and symmetrical

Often classified as a Often classified as a precision forgingprecision forging process process

Flashless forging: (1) just before initial contact with Flashless forging: (1) just before initial contact with workpiece, (2) partial compression, and (3) final punch and workpiece, (2) partial compression, and (3) final punch and die closure.die closure.

Flashless Forging

Forging Hammers (Drop Hammers)Forging Hammers (Drop Hammers)

Apply impact load against workpart Apply impact load against workpart Two types:Two types:

Gravity drop hammers - impact energy from Gravity drop hammers - impact energy from falling weight of a heavy ram falling weight of a heavy ram

Power drop hammers - accelerate the ram Power drop hammers - accelerate the ram by pressurized air or steam by pressurized air or steam

Disadvantage: impact energy transmitted Disadvantage: impact energy transmitted through anvil into floor of building through anvil into floor of building

Commonly used for impression-die forgingCommonly used for impression-die forging

Diagram showing details of a drop hammer for Diagram showing details of a drop hammer for impression‑die forging. impression‑die forging.

Drop Hammer Details

Forging PressesForging Presses

Apply gradual pressure to accomplish Apply gradual pressure to accomplish compression operation compression operation

Types:Types: Mechanical press - converts rotation of drive Mechanical press - converts rotation of drive

motor into linear motion of ram motor into linear motion of ram Hydraulic/Pneumatic press – hydraulic/ Hydraulic/Pneumatic press – hydraulic/

pneumatic piston actuates ram pneumatic piston actuates ram Screw press - screw mechanism drives ram Screw press - screw mechanism drives ram

Upsetting and HeadingUpsetting and Heading

Forging process used to form heads on nails, Forging process used to form heads on nails, bolts, and similar hardware products bolts, and similar hardware products

More parts produced by upsetting than any More parts produced by upsetting than any other forging operation other forging operation

Performed cold, warm, or hot on machines Performed cold, warm, or hot on machines called called headersheaders or or formersformers

Wire or bar stock is fed into machine, end is Wire or bar stock is fed into machine, end is headed, then piece is cut to length headed, then piece is cut to length

For bolts and screws, thread rolling is then For bolts and screws, thread rolling is then used to form threads used to form threads

An upset forging operation to form a head on a bolt or similar 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 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 the stop, (2) gripping dies close on the stock and the stop is retracted, (3) punch moves forward, (4) bottoms to form the retracted, (3) punch moves forward, (4) bottoms to form the head.head.

Upset Forging

Trimming operation (shearing process)Trimming operation (shearing process) to remove the flash after to remove the flash after impression‑die forgingimpression‑die forging..

Trimming After Impression-Die Forging

ExtrusionExtrusion

Compression forming process in which work Compression forming process in which work metal is forced to flow through a die opening metal is forced to flow through a die opening to produce a desired cross‑sectional shape to produce a desired cross‑sectional shape

Process is similar to squeezing toothpaste Process is similar to squeezing toothpaste out of a toothpaste tube out of a toothpaste tube

In general, extrusion is used to produce long In general, extrusion is used to produce long parts of uniform cross sectionsparts of uniform cross sections

Two basic types:Two basic types: Direct extrusionDirect extrusion Indirect extrusionIndirect extrusion

Direct extrusion.Direct extrusion.

Direct Extrusion

Comments on Direct Extrusion Comments on Direct Extrusion

Also called Also called forward extrusionforward extrusion As ram approaches die opening, a small portion of As ram approaches die opening, a small portion of

billet remains that cannot be forced through die billet remains that cannot be forced through die opening opening

This extra portion, called the This extra portion, called the buttbutt, must be , must be separated from separated from extrudateextrudate by cutting it just beyond by cutting it just beyond the die exit the die exit

Starting billet cross section usually roundStarting billet cross section usually round Final shape of extrudate is determined by die Final shape of extrudate is determined by die

opening opening

(a) Direct extrusion to produce a hollow or semi‑hollow cross (a) Direct extrusion to produce a hollow or semi‑hollow cross sections; (b) hollow and (c) semi‑hollow cross sections. sections; (b) hollow and (c) semi‑hollow cross sections.

Hollow and Semi-Hollow Shapes

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

Indirect Extrusion

Advantages of ExtrusionAdvantages of Extrusion

Variety of shapes possible, especially in hot Variety of shapes possible, especially in hot extrusion extrusion Limitation: part cross section must be uniform Limitation: part cross section must be uniform

throughout length throughout length

Grain structure and strength enhanced in Grain structure and strength enhanced in cold and warm extrusion cold and warm extrusion

Close tolerances possible, especially in cold Close tolerances possible, especially in cold extrusion extrusion

In some operations, little or no waste of In some operations, little or no waste of materialmaterial

Hot vs. Cold ExtrusionHot vs. Cold Extrusion

Hot extrusion - prior heating of billet to Hot extrusion - prior heating of billet to above its recrystallization temperature above its recrystallization temperature Reduces strength and increases ductility of Reduces strength and increases ductility of

the metal, permitting more size reductions the metal, permitting more size reductions and more complex shapes and more complex shapes

Cold extrusion - generally used to produce Cold extrusion - generally used to produce discrete parts discrete parts The term impact extrusion is used to The term impact extrusion is used to

indicate high speed cold extrusion indicate high speed cold extrusion

Extrusion RatioExtrusion Ratio

Also called the Also called the reduction ratioreduction ratio, it is defined as , it is defined as

where where rrx x = extrusion ratio; = extrusion ratio; AAoo = cross-= cross-

sectional area of the starting billet; and sectional area of the starting billet; and AAff = =

final cross-sectional area of the extruded final cross-sectional area of the extruded sectionsection

Applies to both direct and indirect extrusionApplies to both direct and indirect extrusion

f

ox A

Ar

Extrusion Cross SectionsExtrusion Cross Sections

Wire and Bar Drawing Wire and Bar Drawing

Cross‑section of a bar, rod, or wire is Cross‑section of a bar, rod, or wire is reduced by pulling it through a die opening reduced by pulling it through a die opening

Similar to extrusion except work is Similar to extrusion except work is pulledpulled through die in drawing (it is through die in drawing (it is pushedpushed through through in extrusion)in extrusion)

Although drawing applies tensile stress, Although drawing applies tensile stress, compression also plays a significant role compression also plays a significant role since metal is squeezed as it passes since metal is squeezed as it passes through die opening through die opening

Drawing of bar, rod, or wire.Drawing of bar, rod, or wire.

Wire and Bar Drawing

Area Reduction in DrawingArea Reduction in Drawing

Change in size of work is usually given by Change in size of work is usually given by area reduction: area reduction:

where where rr = area reduction in drawing = area reduction in drawing

AAoo = original area of work = original area of work

AArr = final work = final work

o

fo

AAA

r

Wire Drawing vs. Bar Drawing Wire Drawing vs. Bar Drawing

Difference between bar drawing and wire Difference between bar drawing and wire drawing is stock size drawing is stock size Bar drawing - large diameter bar and rod Bar drawing - large diameter bar and rod

stockstock Wire drawing - small diameter stock - wire Wire drawing - small diameter stock - wire

sizes down to 0.03 mm (0.001 in.) are sizes down to 0.03 mm (0.001 in.) are possible possible

Drawing Practice and ProductsDrawing Practice and Products

Drawing practice:Drawing practice: Usually performed as cold workingUsually performed as cold working Most frequently used for round cross Most frequently used for round cross

sectionssections Products:Products:

Wire: electrical wire; wire stock for fences, Wire: electrical wire; wire stock for fences, coat hangers, and shopping carts coat hangers, and shopping carts

Rod stock for nails, screws, rivets, and Rod stock for nails, screws, rivets, and springs springs

Bar stock: metal bars for machining, forging, Bar stock: metal bars for machining, forging, and other processes and other processes

Bar Drawing Bar Drawing

Accomplished as a Accomplished as a single‑draftsingle‑draft operation ‑ operation ‑ the stock is pulled through one die the stock is pulled through one die opening opening

Beginning stock has large diameter and is Beginning stock has large diameter and is a straight cylinder a straight cylinder

Requires a batch type operation Requires a batch type operation

Hydraulically operated draw bench for drawing metal bars.Hydraulically operated draw bench for drawing metal bars.

Bar Drawing Bench

Wire DrawingWire Drawing

Continuous drawing machines consisting Continuous drawing machines consisting of multiple draw dies (typically 4 to 12) of multiple draw dies (typically 4 to 12) separated by accumulating drums separated by accumulating drums Each drum (Each drum (capstancapstan) provides proper force ) provides proper force

to draw wire stock through upstream die to draw wire stock through upstream die Each die provides a small reduction, so Each die provides a small reduction, so

desired total reduction is achieved by the desired total reduction is achieved by the series series

Annealing sometimes required between dies Annealing sometimes required between dies to relieve work hardening to relieve work hardening

Continuous drawing of wire.Continuous drawing of wire.

Continuous Wire Drawing

Preparation of Work for DrawingPreparation of Work for Drawing

Annealing – to increase ductility of stockAnnealing – to increase ductility of stock

Cleaning - to prevent damage to work Cleaning - to prevent damage to work surface and draw diesurface and draw die