iii-2 bulk deformation

8/10/2019 III-2 Bulk Deformation

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BULK DEFORMATION PROCESSES

IN METALWORKING

1. Rolling2. Other Deformation Processes Related to

Rolling

3. Forging

4. Other Deformation Processes Related to

Forging

5. Extrusion

6. Wire and Bar Drawing

Bulk Deformation

Metal forming operations which cause significant

shape change by deforming metal parts whose

initial form is bulk rather than sheet

Starting forms:

Cylindrical bars and billets,

Rectangular billets and slabs, and similar

shapes

These processes stress metal sufficiently to

cause plastic flow into desired shape

Performed as cold, warm, and hot working

operations


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Importance of Bulk Deformation

In hot working, significant shape change canbe accomplished

In cold working, strength is increased during

shape change

Little or no waste - some operations are near

net shape or net shape processes

The parts require little or no subsequent

machining

Four 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

opening4. Wire and bar drawing diameter of wire or bar

is reduced by pulling it through a die opening


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Deformation process in which work thickness is reduced by

compressive forces exerted by two opposing 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

The rolling process (specifically, flat rolling).

ROLLING

Basic Rolling Process

Metal is passedbetween two rolls thatrotate in oppositedirections

Friction acts to propelthe material forward

Metal is squeezed andelongates tocompensate for thedecrease in cross-sectional area

Schematic representation of the hot-rolling process, showingthe deformation and recrystallization of the metal being rolled.


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RECRYSTALLIZATION IN HOT ROLLING

One effect of a hot-working rolling operation is thegrain refinement brought about by recrystallization.

The coarse structure is broken up and elongated by

the rolling action. Because of the high temperature,

recrystallization starts immediately and small

grains begin to form. These grains grow rapidly until

recrystallization is complete.

Types of Rolling

Based on workpiece geometry:

Flat rolling - used to reduce thickness of arectangular cross section

Shape rolling - square cross section isformed into a shape such as an I-beam


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Rolled Products

Hot-rolled products have little directionality in theirproperties

Hot-rolled products are therefore uniform and havedependable quality

Surfaces may be rough or may have a surface oxide

known as mill scale in hot rolling Dimensional tolerances vary with the kind of metal and

the size of the product in hot rolling.

Cold-rolled products exhibit superior surface finishand dimensional precision

ROLLING OF STEELFIRST, Steel has been cast into molds (INGOTS).

The ingot remains in molds until the solidification is about

complete and then removed. While still hot, the ingots are

placed in gas-fired furnaces called soaking pits, where they

remain until attaining working temperature of about 1200C.

The ingots are taken to the rolling mill where, because of the

large variety of finished shapes (plates, sheets, bar stock,

structural shapes, orfoils) to be made, they are first hot

rolled into intermediates shapes as blooms (blum, ktk),

billets (billet, ubuk), and slabs (yass ktk).


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INTERMEDIATE SHAPES

-A bloom has a square cross section with a minimumsize of 150 by 150 mm. About 30 passes are required

to reduce a large ingot into a bloom.

-A billet is smaller than a bloom and may have any

square section from 40 mm up to the size of a bloom.

-Slabs may be rolled from either an ingot or a bloom.

They have a rectangular cross-sectional area with a

minimum width of 250 mm and a minimum thickness

of 40 mm. The width is always three or more times

the thickness, which may be as much as 380 mm.Plates, skelp, and thin strips are rolled from slabs.

ROLLING OF STEEL


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Flowchart of Rolling Operations

Flow chart for the production of

various finished and semifinished

steel shapes. Note the abundance

of rolling operations.

Some of the steel products made in a rolling mill.

Rolled Products Made of Steel


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

FLAT ROLLING

FLAT ROLLING

In rolling, the quantity of metal going into a roll and out of it is the

same, but the area and velocity are changed. Thus, stock

enters the rolls with a speed less than the peripheral roll speed.

The metal emerges from the rolls traveling at a higherspeed

than it enters.

Q1= Q2 = A1V1 = A2V2

Q1 = Quantity of metal going into roll ; Q2 = Quantity of metalleaving roll

A1 = area of an element in front of roll; A2 = Area of an element

after roll

V1 = Velocity in element before roll; V2 = Velocity in element after

roll


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Flat Rolling Terminology

Reduction ratio (indirgeme/haddeleme oran) (r) =

ot

dr

where d = draft; to = starting thickness; and tf = final

thickness

fo ttd

SHAPE ROLLING

Work is deformed into a contoured cross section

rather than flat (rectangular)

Accomplished by passing work through rolls

that have the reverse of desired shape

Products include:

Construction shapes such as I-beams,

L-beams, and U-channels

Rails for railroad tracks

Round and square bars and rods


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Rolling Mill Configurations

Various roll configurations

used in rolling operations.


Roll arrangements used in rolling mills. A, Two-high mill, continuous reversing. B,

Four-high mill with backing-up rolls for wide sheets. C, Three-high mill for back-and-

forth rolling. D, Cluster mill using four backing-up rolls.


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Most primary rolling is done in either a two-high reversingmill or a three-high continuous rolling mill.

In the two-high reversing mill the piece passes through the rolls,

which are then stopped and reversed in direction, and the operation

is repeated. At frequent intervals the metal is turned 90 on its side

to keep the section uniform and to refine the metal throughout.

2-high rolling mill

(b) 3-high rolling mill (c) four-high rolling mill

Three-High Rolling Mill and Four-High Rolling Mill


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WHY SMALLER ROLLS?

Smaller diameter rollsproduce less length of

contact for a given

reduction and require less

force to produce a given

change in shape

HOWEVER Smallercross

section provides a reduced

stiffness

Rolls may be prone to flexelastically because they

are only supported on the

ends

The effect of roll diameter on length of contact for a given reduction.

Multiple backing rolls allow even smaller roll diameters

Various configurations of rolling mills: (d) cluster mill

Cluster Mill


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A series of rolling stands in sequence

CONTINOUS (Tandem) Rolling Mill

Continuous (Tandem) Rolling Mills

Billets, blooms, and

slabs are heated and

fed through an

integrated series of

nonreversing rolling

mills Synchronization of

rollers may pose issuesTypical roll-pass sequences used in producing structural shapes.


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Thread Rolling

Bulk deformation process used to form threadson cylindrical parts by rolling them betweentwo dies

Important commercial process for massproducing bolts and screws

Performed by cold working in thread rollingmachines

Advantages over thread cutting (machining):

Higher production rates

Better material utilization

Stronger threads and better fatigueresistance due to work hardening

THREAD ROLLING

Thread-rolling processes: (a) flat dies and (b) two-roller dies.


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

Thread Rolling (FLAT DIES)

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


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Ring rolling used to reduce the wall thickness and increase the diameter

of a ring: (1) start, and (2) completion of process.

Ring Rolling

FORGING (DVME)

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

Forging is adaptable to carbon and alloy steels, wrought

iron, copper, and aluminum and magnesium alloys.

Also, basic metals industries use forging to establish basic

form of large parts that are subsequently machined to final

shape and size


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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: increased strength

that results from strain hardening

Impact vs. press forging:

Forge hammer- applies an impact load

Forge press - applies gradual pressure

HOT FORGING

The number of blows required varies according to

the size and shape of the part, the forging qualities

of the metal, and the tolerances required.

Forging temperature for steel is 1100-1250C.

Advantages of the hot forging operation include a finecrystalline structure of the metal, closing of any voids,

reduced machining time, and improved physical properties.

Disadvantages include scale inclusions and the highcost of dies, which prohibits short-run jobs.


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Types of Forging Dies

Open-die forging - work is compressed betweentwo flat dies, allowing metal to flow laterally with

minimum constraint

Impression-die forging - die contains cavity or

impression that is imparted to workpart

Metal flow is constrained so that flash is created

Flashless forging - workpart is completely

constrained in die

No excess flash is created

(a) open-die forging.

OPEN-DIE Forging


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Open-Die Forging

Compression of workpart between two flat dies Similar to compression test when workpart has

cylindrical cross section and is compressed along

its axis

Deformation operation reduces height and

increases diameter of work

Common names include upsettingor upset

forging

The accuracy of open-die forging is not high and

complicated shapes can not be obtained.

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 workpart height and

true strain is given by:

where ho= starting height; and h = height at some

point during compression

At h = final value hf, true strain is maximum value

h

holn


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Homogeneous deformation of a cylindrical workpart under ideal

conditions in an open-die forging operation: (1) start of process withworkpiece at its original length and diameter, (2) partial compression,

and (3) final size.

Open-Die Forging with No Friction (HAPPENS

ONLY UNDER IDEAL CONDITIONS)

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

Actual deformation of a cylindrical workpart in open-die forging, showing pronouncedbarreling:

(1) start of process, (2) partial deformation, and (3) final shape.


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(Top) Illustration of the

unrestrained flow of

material in open-die

forging. Note the barrel

shape that forms due to

friction between the die

and material.

(Middle) Open-die forging

of a multidiameter shaft.

(Bottom) Forging of aseamless ring by the

open-die method.


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IMPRESSION-DIE Forging

Compression of workpart by dies with inverse of desired part shape

Closed-impression die forgings have better utilization of material than open (flat)dies, better physical properties, closer tolerances, higher production rates, and less

requirement of operator skill.

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

plates. Flash must be later trimmed, but it serves an important function during

compression:

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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Sequence in impression-die forging: (1) just prior to initial contact

with raw workpiece, (2) partial compression, and (3) final die

closure, causing flash to form in gap between die plates.

Impression-Die Forging

Impression-Die Forging

The dies are shaped to control the flow of metal

The die halves are matched and separately attached to the movable ram

and the fixed anvil. The forging is produced by impact or pressure, which

compels the hot and pliable metal to conform to the shape of the dies.

Metal flows and completely fills the die

Schematic of the impression-die forging

process, showing partial die filling andthe beginning of flash formation in the

center sketch and the final shape with

flash in the right-hand sketch.


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Impression-Die Forging Practice

Several forming steps often required, with separate diecavities for each step

Beginning steps redistribute metal for more uniform

deformation and desired metallurgical structure in

subsequent steps and final steps bring the part to final

geometry

First impression is called edging, fullering, or bending

Intermediate impressions are for blocking the metal to

approximately its final shape

Final shape is given in its final forging operation Impression-die forging is often performed manually by

skilled operator under adverse conditions

Impression drop-forging dies

and the product resulting from

each impression. The flash is

trimmed from the finished

connecting rod in a separate

trimming die. The sectional view

shows the grain flow resulting

from the forging process.

Impression-Die Forging Practice separate die cavities


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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 of impression-die forging:

Not capable of close tolerances

Machining often required to achieve accuracies and features needed

Upon completion all forgings are covered with scale (kabuk, tufal) and

must be cleaned. This can be done by pickling in acid (asitletemizleme), shot peening (bilyal dvme), or tumbling (deirmen),

depending on the size and composition of the forgings.

FLASHLESS FORGING

Compression of work in punch and die tooling whose

cavity does not allow for flash

Flashless forging can be performed if the metal is

deformed in a cavity that provides total confinement

Starting workpart volume must equal die cavity volume

within very close tolerance

Process control more demanding than impression-dieforging

Best suited to part geometries that are simple and

symmetrical

Often classified as aprecision forgingprocess


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Three types of forging (c) flashless forging.

Flashless Forging

Flashless forging: (1) just before initial contact with workpiece, (2)

partial compression, and (3) final punch and die closure.

Flashless Forging


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Forging Hammers (Drop Hammers)(ahmerdanda dvme, serbest dvme)

Apply impact load against workpart

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

The two principal types of drop-forging hammers are the gravity drop (dm ahmerdan)

and the steam hammer (buharahmerdan). In the gravity-type hammer, the impact pressure

is developed by the force of the falling ram as it strikes upon the lower fixed die. It utilizes air

or steam to lift the ram. In the steam hammer the ram and hammer are lifted by steam, and

the force of the blow is controlled by throttling the steam. These hammers operate at over 300

blows/min. The capacity of steam hammers range from 2-200 kN (i.e. up to 20 t force).

Disadvantage: impact energy transmitted through anvil into

floor of building

Commonly used for impression-die forging

Drop forging hammer, fed by conveyor and heating units at the right of the

scene

Forging Hammers (Drop Hammers)


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

Forging Hammers (Drop Hammers)Details

Forging Hammers (Drop Hammers)

(Left) Double-frame drop hammer. (Right) Schematic diagram

of a forging hammer.


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Forging Presses (stroke restricted machines)(presle dvme)

Apply gradual pressure to accomplish compression operation

Press forging is used for large or thick products

Slow squeezing action penetrates completely through the metal.

Press forging employs a slow squeezing action in deforming the

plastic metal as contrasted to the rapid impact blows of a hammer.

Produces a more uniform deformation and flow

Longer time of contact between the die and workpiece

Dies may be heated (isothermal forging)

Presses are vertical type and either mechanically or hydraulically

operated.

Types:

Mechanical press - converts rotation of drive motor into linear motion of

ram. Faster

Hydraulic press - hydraulic piston actuates ram. More controllable

Screw press - screw mechanism drives ram

For small press forgings closed-impression dies are used,

and only one stroke of the ram is normally required to perform

the forging operation.

In the forging press a greater proportion of the total energy

input is transmitted to the metal than in a drop hammerpress.

Much of the impact of the drop hammer is absorbed by the

machine and foundation.

Most press forgings are symmetrical in shape with surfaces that

are smooth, and they provide a closer tolerance than is

obtained by a drop hammer. However, many parts of irregular

and complicated shapes can be forged more economically by

drop hammers. Forging presses are often used for sizing

operations on parts made by other processes.

Forging Presses


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UPSET FORGING (yma, iirme)

Upset Forging is used to form heads on nails, bolts,and similar hardware products. It increases the

diameter of a material by compressing its length

More parts produced by upset forging 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 toform threads

UPSET FORGING (Heading)

Upset forging entails gripping a bar of uniform section in dies and applying

pressure on the heated end, causing it to be upset or formed to shape.

The length of the stock to be upset cannot be more than two or three times

the diameter or else the material will bend rather than bulge out to fill the die

cavity.


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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 (Heading)

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.

Upset Forging (Heading)


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Upset Forging Rules

RULE 1: The length of the unsupported material that can be gathered or upset in one blow without injurious bucklingshould be limited to three times the diameterof the bar.RULE 2: Lengths of stock greater than three times the diameter may be upset successfully provided that the diameterof the upset is not more than 1 times the diameterof the bar.RULE 3: In an upset requiring stock length greater than three times the diameter of the bar, and where the diameterof the cavity is not more than 1 times the diameter of the bar (the conditions of rule 2), the length of the unsupportedmetal beyond the face of the diemust not exceed the diameterof the bar.

Swaging

Accomplished by rotating dies that hammer a workpiece radially

inward to taper it as the piece is fed into the dies

Used to reduce diameter of tube or solid rod stock

Mandrel sometimes required to control shape and size of

internal diameter of tubular parts

Swaging process to reduce solid rod stock; the dies rotate as they hammer the work In

radial forging, the workpiece rotates while the dies remain in a fixed orientation as they

hammer the work.


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Swaging

Also known as rotary

swaging and radial

forging

Uses external

hammering to reduce

the diameter or produce

tapers or points on

round bars of tubes Schematic of the roll-forging process showing the two shaped rollsand the stock being formed.

Swaging

Tube being

reduced in

a rotary

swaging

machine.

Basic components and motions of a rotary swaging machine.

(Note: The cover plate has been removed to reveal the interior

workings.)

A variety of swaged parts, some with internal details.


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Roll Forging

Round or flat bar stock isreduced in thickness and

increased in length

Produces products such

as axles, tapered levers,

and leaf springs

Little or no flash is

produced

Rolls from a roll-forging machine and the various

stages in roll forging a part.

Roll-forging machine in operation

Trimming

Cutting operation to remove flash from workpart

in impression-die forging

Usually done while work is still hot, so a

separate trimming press is included at the

forging station

Trimming can also be done by alternative

methods, such as grinding or sawing


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Trimming operation (shearing process) to remove the flash after

impression-die forging.

Trimming After Impression-Die Forging

EXTRUSION

Compression forming process in which work metal is forced to flow

through a die opening to produce a desired cross-sectional shape

Some metals, notably lead, tin, and aluminum, may be extruded cold,

whereas others require the application of heat to render them plastic

or semisolid before extrusion.

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

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

Rods, tubes, molding trim, structural shapes, brass cartridges (fiek),

and lead-covered cables are typical products of metal extrusion.

Two basic types:

Direct extrusion

Indirect extrusion


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EXTRUSION

Almost unlimited lengths of a continuous cross section can

be produced, and because of low die costs production runs of

150 m may justify its use.

Typical

shapes

produced

by

extrusion

EXTRUSION TYPES

Direct extrusion Solid ram drives the entire billet to and through a stationary die

In direct extrusion, the ram and billet both move and friction betweenthe billet and the chamber opposes forward motion.

Must provide power to overcome friction

Indirect extrusion A hollow ram pushes the die back through a stationary, confined billet

For indirect extrusion, the billet is stationary. There is no billet-

chamber friction, since there is no relative motion.


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Direct extrusion.

Direct Extrusion

A heated round billet is placed into the die chamber andram placed into position. The metal is extruded through

the die opening until only a small amount remains.

Direct Extrusion

Metal is compressed andforced to flow through ashaped die to form aproduct with a constantcross section

May be performed hot orcold

A ram advances from oneend of the die and causesthe metal to flow plasticallythrough the die

Commonly extruded metals:aluminum, magnesium,copper, and lead

Direct extrusion schematic showing the

various equipment components.


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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


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(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 in Direct

Extrusion

Direct Extrusion of Hollow Shapes

Mandrels may be

used to produce

hollow shapes or

shapes with multiple

longitudinal cavities

Two methods of extruding hollow shapes using internal mandrels. In part (a) the

mandrel and ram have independent motions; in part (b) they move as a single unit.


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

section.

INDIRECT EXTRUSION

Indirect extrusion is similar to direct extrusion except that the extruded part is forced

through the ram stem. Less force is required by this method because there is no

frictional force between the billet and the container wall. The weakening and

complexity of the ram when it is made hollow and the difficulty of providing good

support for the extruded part constitute limitations of this process.

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


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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


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Extrusion Ratio

Also called the reduction ratio, it is defined as

where rx = extrusion ratio;Ao = cross-sectional

area of the starting billet; andAf = final cross-

sectional area of the extruded section

Applies to both direct and indirect extrusion

f

ox

A

Ar

(a) Definition of die angle in direct extrusion; (b) effect of die angle on ram

force.

Extrusion Die Features

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.


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Orifice Shape of Extrusion Die

Simplest cross section shape is circular dieorifice

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

Extrusion Presses

Either horizontal or vertical

Horizontal more common

Extrusion presses - usually hydraulically

driven, which is especially suited to

semi-continuous direct extrusion of long

sections

Mechanical drives - often used for coldextrusion of individual parts


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Forces in Extrusion

Lubrication is important

to reduce friction and

act as a heat barrier

Metal flow in extrusion

Flow can be complex

Surface cracks, interior

cracks and flow-related

cracks need to be

monitored Process control is

importantDiagram of the ram force versus ram position for both

direct and indirect extrusion of the same product. The

area under the curve corresponds to the amount of

work (force x distance) performed. The difference

between the two curves is attributed to billet-chamber

friction.

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 ispushedthrough in extrusion)

Although drawing applies tensile stress, compression also

plays a significant role since metal is squeezed as it passes

through die opening


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Wire, Rod, and Tube Drawing

Schematic drawing of the rod-or bar-drawing process.

Cold-drawing smaller tubing from larger tubing. The die

sets the outer dimension while the stationary mandrel

sizes the inner diameter.

Tube drawing with a floating plug.

Schematic of wire

drawing with arotating draw block.

The rotating motor on

the draw block

provides a

continuous pull on

the incoming wire.

Area Reduction in Drawing

Change in size of work is usually given by area

reduction:

where r= area reduction in drawing;Ao

=

original area of work; andAr= final work

o

fo

A

AAr


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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

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


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Bar Drawing

Accomplished as a single-draftoperation - the stock ispulled through one die opening

Beginning stock has large diameter and is a straight

cylinder

Requires a batch type operation

Hydraulically

operated drawbench for drawing

metal bars.

Bar Drawing Bench

Wire Drawing

Wire is made by cold-drawing hot-rolled wire or rod through one or

more dies to decrease its size and increase the physical properties.

Continuous drawing machines consisting of multiple draw dies

(typically 4 to 12 successive dies) separated by accumulating

drums. The end is grasped by tongs (maa, ene) on a drawbench

and pulled through to such length as may be wound around a

drawing block or reel. The number of dies in the series will depend

on the kind and final diameter of metal or alloy being processed.

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 to relieve work

hardening


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WIRE DRAWING

Wire Drawing machine and a drawing reel

Schematic of a multistation synchronized wire-drawing machine. To prevent accumulation or

breakage, it is necessary to ensure that the same volume of material passes through each station in a

given time. The loops around the sheaves between the stations use wire tensions and feedback

electronics to provide the necessary speed control.

Cross section through a typical carbide

wire-drawing die showing the

characteristic regions of the contour. The

dies are usually made from tool steels or

tungsten carbide, although diamond dies

can be used for drawing small diameters.

WIRE DRAWING


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WIRE DRAWING

Wire drawing is often determined by the followingrelationships:

Reduction in area (r) [%] = ((Ao - Af)/Ao)x100

where Ao and Afare the original and final area of the

wire.

Features of a Draw Die

Entry region - funnels lubricant into the die to prevent scoring of work

and die

Approach - cone-shaped region where drawing occurs

Bearing surface - determines final stock size

Back relief - exit zone - provided with a back relief angle (half-angle) of

about 30

Draw die for

drawing of

round rod or

wire


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Preparation of Work for Drawing

Annealing to increase ductility of stock Cleaning - to prevent damage to work surface and

draw die

Pointing to reduce diameter of starting end to

allow insertion through draw die

IMPACT EXTRUSION

Impact Extrusion (svama ekstrzyon): In impact extrusion a

punch is directed to a slug (or blank) (taslak) with such a force

that the metal from the slug is pushed up and around it.

Most impact extrusion operations, such as the manufacture of

collapsible tubes (shaving cream, toothpaste, paint pigment

tubes) are cold-working ones.

Production

of

toothpaste

tube by

impact

extrusion


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Impact Extrusion

A metal slug ispositioned in a diecavity where it is struckby a single blow

Metal may flow forward,backward or somecombination

The punch controls theinside shape while thedie controls the exteriorshape Backward and forward extrusion

with open and closed dies.

Impact Extrusion

Steps in the forming of a bolt by cold extrusion, cold heading, and thread rolling.

(a) Reverse

(b) Forward

(c) Combined

forms of cold

extrusion.

Forming a Bolt with Cold-Forming Sequence


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Cold-forming sequence involving cutoff, squaring, two

extrusions, an upset, and a trimming operation.

Typical parts made by upsetting and related operations.

Cold-Forming Sequence Examples

Piercing

Thick-walled seamless tubing can be made by rotarypiercing

Heated billet is fed into the gap between two large,convex-tapered rolls

Forces the billet to deform into a rotating ellipse

Principle of the

Mannesmann process

of producing seamless

tubing.


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Other Squeezing Operations

Hubbing a die block in a hydraulic press. Inset shows

close-up of the hardened hub and the impression in the

die block. The die block is contained in a reinforcing ring.The upper surface of the die block is then machined flat

to remove the bulged metal.

The

coining

process.

Summary

There are a variety of bulk deformation

processes

The main processes are rolling, forging,

extrusion, and drawing

Each has limits and advantages as to its

capabilities

The correct process depends on the desiredshape, surface finish, quantity, etc.

iii-2 bulk deformation

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