Forming process

7/26/2019 Forming process

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Cha ter 16:

Bulk Formin Processes

Bulk Deformation

"Bulk" refers to workparts with relatively low

- - Si nificant sha e chan e

Starting forms:

Cylindrical bars and billets,

Rectangular billets and slabs

Plastic flow o , warm, an o wor ng

Introduction

Forging, rolling, and wire drawing were

The Industrial Revolution allowed theseprocesses to be done at a higher level

ecen y, many processes ave egun o e

automated

Processes

Bulk deforming processes can be classified as

Primary processes reduce a cast material into slabs (, , , Secondary processes reduce shapes into finished or

Bulk deformation - thickness or cross sections are

Sheet-forming - thickness and cross section remainrelatively constant


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Bulk Deformation Processes

Rolling () Forging

Wire, rod, and tube drawing () Cold forming, cold forging, and impact

Piercing

Squeezing processes

Rollin

Slab or plate is squeezed between opposing

Rollin o erations reduce the thickness or

change the cross section of a material

Thick stock can be rolled into blooms, billets,

or slabs

Startin Stock

Blooms have a square or rectangular cross

Billets are usuall smaller than a bloom andcan have a square or circular cross section

Slabs are a rectangular solid with a width

greater than twice the thickness

, ,

Flowchart of Rollin O erations

Fi ure 16-1 Flow chart for

the production of variousfinished and semifinished

steel shapes. Note the

operations. (Courtesy of

American Iron and Steel

Institute, Washington,

D.C.)


3/17

Basic Rollin Process x

Metal is passedbetween two rolls thatrotate in oppositedirections

Friction acts to propelthe material forward

Metal is squeezed andelon ates to

compensate for thedecrease in cross- Figure 16-2 Schematic representation of the hot-

sectional arearolling process, showing the deformation and

recrystallization of the metal being rolled.

Widenin of Material

Rollin Mill Confi urations

Figure 16-3 Variousroll configurations

used in rollingoperations.

us er ro s suppor sma er con ac ng

rolls

(Source: www.elgiloy.com)


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Rollin Mill Confi urations

Smaller diameter rolls

roduce less len th of

-

of contact for a given reduction.

contact for a given

reduction and require less

force to produce a given

change in shape

ma er cross sec on

provides a reduced stiffness

y x

elastically because they areonl su orted on the ends

Continuous Tandem Rollin Mills

Billets, blooms, and x

fed through an

nonreversing rolling

Synchronization of

rollers Figure 16-5 Typical roll-pass sequences used in.

Roll Formin hot : I-beams

u y , y

C. Ebbets, http://en.wikipedia.org/)

(Source: Kalpakjian, 2007)

Rin Rollin

Deformation process in

which a thick-walled rin

x

of smaller diameter is

rolled into a thin-walled

ring of larger diameter

Produces seamless rin s

Circumferential grain

orientation and is used in

rockets, turbines, airplanes,

pressure vessels, andFigure 16-6 Schematic of horizontal ring rolling

pipelines. ,

its diameter will increase.


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Thread Rollin

van ages over rea cu ng mac n ng : Higher production rates

Stronger threads and better fatigue resistance due to work

hardenin

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

(Source: Groover, 2005)

Machined and Rolled Threads


Precision of Rolled Products

Hot-rolled products have little directionality in

Hot-rolled products are therefore uniform andave epen a e qua y

Surfaces may be rough or may have a surfaceoxide known as mill scale

Dimensional tolerances var with the kind of metal and the size of the product

-finish and dimensional precision

Flatness Control and Rollin Defects x

Rollers must be evenly

perfectly flat pieces to Fi ure 16-7 above a Loadin on a rollin mill

Sometimes thisroll. The top roll is pressed upward in the centerwhile being supported on the ends. (b) The

elastic response to the three-point bending.

var a on n ro er

flatness may be

desired

- roll flexure. When the roll flexes in three-point bending,

the crowned roll flexes into flatness.


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For in

Work is squeezed and shaped between

Processes that induce plastic deformationroug oca ze compress ve orces app e

through dies

Parts can range in size

Upset () Squeezed in closed impression dies

O en-die Hammer For in

Same type of forging done by a blacksmith

operation

An impact is delivered by some type of

Simplest industrial hammer is a gravity drop

machine () -

varying blows

O en-die Hammer For in

Fi ure 16-9 Left Double-frame dro hammer.(Courtesy of Erie Press Systems, Erie, PA.)

(Right) Schematic diagram of a forging hammer.

x

-

Illustration of theunrestrained flow of

material in open-die

forging. Note thebarrel shape that

forms due to friction

material. (Middle)

Open-die forging of amultidiameter shaft.(Bottom) Forging of a

seamless ring by the

open-die method.

Courtes of For inIndustry Association,

Cleveland, OH.)


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Im ression-Die Hammer For in

The dies are shaped to control the flow of metal

piece to the anvil

Metal flows and completely fills the die x

Figure 16-11 Schematic of the- ,

showing partial die filling and the

beginning of flash formation in thecenter sketch and the final shape

with flash in the right-hand sketch.

Im ression-Die Hammer For in

Excess metal may squeeze out of the die

Flashless forging can be performed if the metal is

e orme n a cav y a prov es o a con nemen

Many forged products are produced with a series of

cavities

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

x

Figure 16-12

Impression drop-forging

es an e pro uc

resulting from each

impression. The flash istrimmed from the

finished connecting rod

in a separate trimming

die. The sectional views ows e gra n ow

resulting from theforging process.

(Courtesy of Forging

Industry Association,

Cleveland, OH.)

Press For in

Press forging is used for large or thick

Slow s ueezin action enetrates com letelthrough the metal

Longer time of contact between the die and

workpiece

Presses are either mechanical or hydraulic


8/17

-

and Associated Tooling Forging dies are typically made of high-alloy or tool

steel

Rules for better and more economical parts: Dies should art alon a sin le flat lane or follow the contour of

the part

Parting surface should be a plane through the center of the

Adequate draft

Generous fillets and radii

Ribs should be low and wide

Various cross sections should be balanced

Full advanta e should be taken of fiber flow lines

Dimensional tolerances should not be closer than necessary

Im ression-Die For in s

Important design details

Number of intermediate steps

Shape of each step

Amount of excess metal to fill the die

Dimensions of flash at each step

Good dimensional accuracy

Figure 16-15A forged-and-

machined automobile

been formed from

microalloyed steel.

Performance is superior tocranks of cast ductile iron.

U set For inBolt manufacture


U set For in

Increases the diameter of a material by compressing its length

Both cold and hot upsetting

Three rules of upset forging

1. The length of the unsupported material that can be gathered or

times the diameter of the bar.

2. Lengths of stock greater than three times the diameter may beupse success u y prov e a e ame er o e upse s no morethan 1 times the diameter of the bar.

3. In an upset requiring stock length greater than three times theameter o t e ar, an w ere t e ameter o t e cavty s not more

than 1 times the diameter of the bar (the conditions of rule 2), thelength of the unsupported metal beyond the face of the die must notexcee e ame er o e ar.


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U set For in x

Figure 16-17 Schematics illustrating the rules governing upset forging. (Courtesy of National

Machinery Company, Tiffin, OH.)

Automatic Hot For in

Slabs, billets, and x

blooms can be slid into

one end of a room and

hot-forged products canemerge at the other

end, with every process

automated

- - - .

The sheared billet is progressively shaped into an upset pancake, blocker forging, and finished gearblank. (b) Samples of ferrous parts produced by automatic hot forging at rates between 90 and 180

parts per minute. (Courtesy of National Machinery Company, Tiffin, OH.)

Roll For in

Round or flat bar stock

and increased in length ro uces pro uc s

such as axles, tapered

evers, an ea spr ngs

Little or no flash is

produced

- - .(Right) Rolls from a roll-forging machine and the

various stages in roll forging a part. (Courtesy of AjaxManufacturing Company, Euclid, OH)

x

Figure 16-20 Schematic of the roll-forging processshowing the two shaped rolls and the stock being

formed. (Courtesy of Forging Industry Association,

, .


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Swa in

Also known as rotary swaging () and radialfor in

Accomplished by rotating dies that hammer a workpiece


Swa in Fi ure 16-21 Below Tube bein reduced in arotary swaging machine. (Courtesy of the Timkin

Company, Canton, OH.)

Figure 16-23 (Below) A variety of swaged parts,

some with internal details. (Courtesy of Cincinnati

acron, nc. nc nna , .

Figure 16-22 (Right) Basic components and motions

of a rotary swaging machine. (Note: The cover plate

has been removed to reveal the interior workings.), , .

-

Near-Net-Shape Forging

80% of the cost of a forged-part can be due

-

To minimize ex ense and waste artsshould be forged as close the final shape as

These processes are known as net-shape or

precision forging

bar stock; (right) by cold forming. Note the reduction in waste.

(Courtesy of National Machinery Co.)


11/17

Unit Cost in For in Relative Unit Costs of a Small

Connecting Rod


(Source:)

Extrusion

Metal is compressed andforced to flow through a

x

shaped die to orm a

product with a constant

May be performed hot orcold

Commonly extruded metals:aluminum, magnesium,copper, an ea

Figure 16-25 Direct extrusion schematic showing

the various equipment components. (Courtesy of

Danieli Wean United, Cranberry Township, PA.)


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T ical Extruded Products

Figure 16-26 Typical shapes produced by extrusion. (Left) Aluminum products. (Courtesy of

Aluminum Company of America, Pittsburgh, PA.) (Right) Steel products. (Courtesy of AlleghenyLudlum Steel Corporation, Pittsburgh, PA.)

Advanta es of Extrusion

Many shapes can be produced that are not

No draft is required

Amount of reduction in a single step is onlylimited b the e ui ment not the material orthe design

Small quantities of a desired shape can beproduced economically

Extrusion Methods

Direct extrusion

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

Must provide power to overcome friction

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

billet

Figure 16-27 Direct and indirect extrusion. In direct extrusion, the ram and billet both move andfriction between the billet and the chamber opposes forward motion. For indirect extrusion, the billet is

stationary. There is no billet-chamber friction, since there is no relative motion.

Forces in Extrusion

Lubrication is important

act as a heat barrier e a ow n ex rus on

Flow can be complex

Surface cracks, interior

cracks and flow-related

crac s nee o e

monitored Figure 16-28 Diagram of the ram force versus ramposition for both direct and indirect extrusion of the

same product. The area under the curve correspondsto the amount of work (force x distance) performed.

The difference between the two curves is attributed to

billet-chamber friction.


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Extrusion Die Features

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

angle on ram force. (Source: Groover, 2005)

Extrusion of Hollow Sha es

x

Mandrels () may

hollow shapes or

longitudinal cavities

Fi ure 16-30 Two methods of extrudin hollow sha es usin internal mandrels. In art a the

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

H drostatic Extrusion

g -pressure u surroun s

the workpiece and applies the

force to execute extrusion

x

Billet-chamber friction is

eliminated High efficiency process

Pressure induced ductility -

r e ma er a s can e

extruded

because the fluid acts as a

heat sink

Figure 16-32 Comparison of conventional (left)

and hydrostatic (right) extrusion. Note the

- Seals must be designed to

keep the fluid from leaking

-and miter-ring seals on both the die and ram.

Defects

Centerburst Piping Surface cracking



14/17

Wire Rod and Tube Drawin

Reduce the cross section of a material by

Similar to extrusion but the force is tensile x x

Figure 16-34 Schematic drawing of the rod-or bar-drawing process.

Figure 16-36 Cold-drawing smaller tubing

from larger tubing. The die sets the outer

dimension while the stationary mandrel sizes.

Drawin Practice and Products

Drawing practice:

Most frequently used for round cross sections

ro ucts: Wire: electrical wire; wire stock for fences, coat

hangers, and shopping carts

Rod stock for nails, screws, rivets, and springs

Barstock: metal bars for machining, forging, andother processes

Tube and Wire Drawin x

Tube sinking does not

Internal diameter

cost and a floating plug is

used Figure 16-37 (Above) Tube drawing witha floating plug.

Figure 16-38 Schematic of wire drawing with arotating draw block. The rotating motor on the

draw block provides a continuous pull on the

incoming wire.

Figure 16-39 Cross section

wire-drawing die showing thecharacteristic regions of the

contour.

x

Figure 16-40 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.


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Pre aration of Work for Drawin

Annealing - to increase ductility of stock

-

and draw die

-

to allow insertion through draw die

Impact Extrusion Slugs of material are

s ueezed into or

extruded from shapeddie cavities to producefinished parts of preciseshape and size

Cold heading (/) is a form ofupset forging Used to make the

- -

heading operation.

enlarged sections on theends of rod or wire (i.e.

, , .

Im act Extrusion

A metal slug isositioned in a die

x

cavity where it is struck

by a single blow Metal may flow forward,

backward or somecombination

The unch controls theinside shape while the

die controls the exterior

Figure 16-43 Backward and forward extrusion

shape .

Cold ExtrusionFigure 16-44 (a)Reverse (b)

combined forms of

cold extrusion.

(Courtesy the

AluminumAssociation,

Arlington, VA.)

Figure 16-45

(Right) Steps in

the forming of a

bolt by cold,

heading, and

thread rolling.(Courtesy of

National

Machinery Co.Tiffin, OH.)


16/17

Figure 16-46 Cold-forming sequence involving Figure 16-47 Typical parts made by upsetting, , , ,

trimming operation. Also shown are the finishedpart and the trimmed scrap. (Courtesy of National

Machinery Co., Tiffin, OH.)

.Machinery Co., Tiffin, OH.)

PiercinSeamless pipe, tube

Thick-walled seamless tubing can be made by rotaryiercin

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

Forces the billet to deform into a rotating ellipse

Figure 16-50 (Left)

Principle of the

Mannesmann process ofproducing seamless tubing.

(Courtesy of AmericanBrass Company, Cleveland,

.

crack formation in the

Mannesmann process.

Other S ueezin Processes

Roll extrusion- thin walled cylinders are producedfrom thicker-wall c linders

-of material by forming an expanded head on the

a ng-permanen y o ns par s oge er w en asegment of one part protrudes through a hole in the

Other S ueezin Processes x

Figure 16-51 The

roll-extrusion process:

(a) with internalrollers expanding the

with external rollersreducing the outer

diameter.

x

.

Figure 16-52 Joining

Figure 16-54

Permanentlyattaching a shaft

componen s y r ve ng. o a p a e y

staking.


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Other S ueezin O erations

Coining ()- cold-

squeezing of metal

while all of the surfaces

x

- .

are confined within aset of dies

Hubbing- plastically

forms recessed cavities

in a workpiece

Figure 16-56 Hubbing a die block in a hydraulic

press. Inset shows close-up of the hardened huband the impression in the die block. The die blockis contained in a reinforcin rin The u er .

surface of the die block is then machined flat to

remove the bulged metal.

Processing

Deformation processes can be used to improve or

Peening ()- mechanical working of surfacesy repea e ows o mpe e s o or a roun -nose

tool

Burnishing- rubbing a smooth, hard object under

pressure over the minute surface irregularities

Roller burnishing- used to improve the size and

surfaces

(Source: )

Summar

There are a variety of bulk deformation

The main rocesses are rollin for inextrusion, and drawing

ac as m s an a van ages as o s

capabilities

The correct process depends on the desired

, , , .

Forming process

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